I recently wrote:
and was corrected by my very pedantic South African friend as
Is he right? Am I wrong? Does this vary by region/culture (we are in the U.S.)?
This website seems to suggest that the latter is the correct. Personally, I would have written it the way you have.
I would say “with **my ** telling Gary.”
Antiopodes, but it would vary here too, depending on preference. I might even say “me” if I was being linguistically lazy that day. But I’d feel it was wrong.
It depends on whether the ME belongs to to “You forsee/ Me telling” or “My action of telling Gary”
I’m really looking forward to the grammar experts take on this.
It “should” be ‘my’ because ‘telling’ is used here as a gerund and not a participle. A gerund phrase is essentially treated as a noun, while the gerund within that phrase can be treated as a verb. Here ‘my’ is an modifier of the phrase ‘telling Gary that.’ ‘Me’ can not be a modifier in that way.
However, as any good descriptive linguist (not I) will tell you, certain percentages of English-speaking populations will say it in various ways. “Correct” can be considered a relative term in linguistics, and is not easily pinned down.
Let us not degenerate this thread into another descriptive/prescriptive debate. The OP is looking for a pedantic rule.
Both are correct. It depends entirely on what you want to emphasize. But if you consult a good book like the Merriam-Webster Dictionary of English Usage, it provides a few more notes about it.
First, if a pronoun is used, it’s probably the possessive pronoun (though “her” and “her” are, of course, Indistinguis- er, rather, they’re impossible to tell apart). An accusative pronoun can still be used if the author really wants to emphasize it instead of the gerund. If it’s not a pronoun, again, both forms (possessive and uninflected nouns) are used. Interestingly, the possessive does not predominate in nouns like it does in pronouns, and when sentences become more complex, with modifiers and so on, possessives are even less likely to be used.
If you want a strict rule, then feel free to follow Randy Seltzer’s advice. But if you want to stick to your guns, feel free to do so, because you’re not wrong.
From what I’ve read and heard, this debate would be meaningless in Scouse.
As for “my telling…” vs. “me telling…”, I would probably say “me” in any informal context, but in a formal setting I would say “my”. It’s another one of those things like “who” and “whom”.
Suddenly, I stopped in my tracks. “A calling”, I announced. “I am needed”. But just as I prepared to race in search of the source, the sensation subsided.
Now I understand. It’s like flashing the bat-signal with only one wing. 
I’m not starting a debate here (this isn’t the place, anyway), I just want to clarify my purpose in contributing to language threads.
I’m not at all opposed to people offering good prescriptive advice. When prescriptivism is properly done, in fact, it has no bearing whatsoever on descriptive linguistics. Describers say how the language is, and prescribers say how the language should be used, and when both groups are working within their respective fields, there need not be any contradictions in what they say.
But the OP asked “Am I wrong?”. It is possible that the OP wants strict, pedantic advice on how the language should be used. Many people want such advice, and many also want it couched in false absolutist terms, as amply demonstrated by the popularity of books like the shitty Strunk & White and the pretty good Garner’s. But even if that’s true, every OP who starts a GQ thread about language on the SDMB should still be fully informed about the facts of the topic before they’re given specific opinions on what’s best.
This is especially important when the question is about a topic, like this OP, where the opinions wildly diverge. The earliest commentators, largely using Latin in their attempt to understand English (the poor misguided bastards), came to the exact opposite conclusion of pulykamell’s cite and your own offering. And to get all historical on this baby, the arguments raged for a couple hundred years with no end in sight. It’s funny that even a gathering of the most pedantic of the pedants couldn’t agree on this issue.
That fact that some people now seem to prefer the possessive isn’t based on any more evidence than originally. Fowler came down in support of the possessive essentially because he liked it better (though he had a tendency to believe that his preferences were holy writ), and the prescriptivists pretty much dig Fowler, and it seems that now the possessive has a bigger fanbase than it used to. But again, this is based on a few people’s opinions and not on the facts of centuries of usage, which clearly indicate that both forms are used, often even by the very same distinguished writer on the very same page.
What this means is that the OP has a choice. And to strip away that choice is not only factually incorrect (“me” can definitely be put before a gerund), it is also poor prescriptive advice. To arbitrarily take away choices bothers me not only because it isn’t how the language works, but it also takes away the beauty and flexibility of English. fighting ignorant, under the real rules of English as spoken by real speakers every day, can absolutely choose to emphasize himself by using “me” instead of emphasizing “Gary”. In another situation, when the OP might want to emphasize “Gary” instead of “Steve” or “Sally” or whoever, the OP might say “my” so naturally and effortlessly and unconsciously that it could go completely unnoticed.
That fact that this isn’t set in stone, that there is some give’n’take based on context, gives our language wondrous adaptability.
So no, I’m not really bothered by people giving prescriptive advice. I’m bothered by people giving bad prescriptive advice, especially when they neglect to inform themselves on the issue. This bad stuff includes not only advice that directly contradicts how the majority of people speak, but also stylistic issues that I disagree about. And I mean you no disrespect, but in my opinion (and it’s just an opinion), your advice was bad. It limited the OP’s options unnecessarily, and it did so without giving the historical background that a GQ thread deserves, whether the OP wants to hear the facts or not. But I find no fault with the act of advice-giving itself.
So by all means, please continue to give prescriptive opinions, just as you did. And please continue to acknowledge them for what they are, just as you did. I believe there’s plenty of room for preferences, even in GQ, after the factual question has been answered. Just don’t be surprised if someone calls you on it if your opinion doesn’t mesh with reality.
And just to note my own stylistic travesties, let me point to “That fact that”. I have no idea why I was writing that, but I did it twice. Weird.
I’m surprised nobody else has caught this, but…
…In the above sentence, using “me” implies that “me” is an indirect object.
Using “my” makes “my telling Gary that” the indirect object.
In the former case, “telling Gary that” would be a fragment, so you have to go with option 2.
Or option 3 - next time, just say “Let me know if you have a problem with what I told Gary.” 
This is a very illustrative situation: if your theoretical grammar (i.e., your hypothesized rules for the working of some language) causes you to classify a particular construction as malformed, yet the empirical evidence shows that construction to be regularly and mundanely used without comment, then your theoretical grammar has been shown to be lacking (the same way theories in physics can be shown to be lacking with sufficient experimental evidence; it would be backwards, of course, to insist that the theory was correct and the physical world was just doing the wrong thing in failing to conform). Modification of that hypothesized grammar is therefore recommended (just as physicists were willing to augment the Newtonian theories towards greater accuracy using the results from later discoveries).
Use the possessive pronoun before gerunds if you want to please most English teachers.
Gerunds are verbs used as nouns. They end in “ing.”
Language isn’t a moral issue; me wouldn’t be “wrong.” But for now it would be inelegant. In Dr. Hazlewood’s class, it would be INCORRECT!
That is all that really matters.
I’m with Really Not All That Bright. Both sound awkward to me. Bright’s rewrite works for me.
The two different phrasings stress different things.
“Let me know if you foresee any problems with me telling Gary that.”
As opposed to Joe telling Gary. The problem would occur due to the fact that you’re telling Gary. It’d be OK if Joe told him.
“Let me know if you foresee any problems with my telling Gary that.”
The problems would occur by telling Gary in the first place.
Without context, it’s hard to be sure, but it does look like the second is marginally better, but not so clearly an improvement that it’s worth correcting.
“Me” is common in casual speech, but in formal writing, “my” is correct.
“Telling” is the object of the preposition “with.”
Simplifying the sentence:
You / do have / problem / with telling.
You is the subject
Do have is the verb
Problem is the direct object
With telling is a prepositional phrase modifying the direct object
“My” is an adjective modifying “telling.”
Note how this sentence is different from –
“Do you have a problem with me?”
Here, me is the object of the preposition with.
There are excellent responses above, which I have no hope of competing against quality-wise. I will offer my take on interpretation, though, and perhaps a linguist can describe what I’m trying to say.
“Let me know if you foresee any problems with me telling Gary that.” I always look as this as a dropped “for,” rather like a contraction. In my mind, I understand something like this: “Let me know if you foresee any problems with me for telling Gary that.” The problem you might have is with me, for having told Gary something. It’s me that you object to.
“Let me know if you foresee any problems with my telling Gary that.” This is the construction I would normally use m’self. Of course, the problem you have isn’t so much with me personally, but with my having told Gary something. It’s the telling that you object to.
On the other hand I deplore most poetry because I tend to try to interpret things in a logical, organized manner, and so I may be falsely attributing what I consider a careful distinction upon people who are merely being sloppy in how they speak, i.e., to lots of people they might mean the very same thing with no subtle distinctions.
So you’re saying that if a sizeable minority of English speakers start using “Who is you?” to mean “Who are you?”, we should agree that the second is an acceptable conjugation of to be?
Well, yes, at least in the dialect of those speakers who use it that way. Why not? Same as we accept “Who are you?” now in situations where we once might have demanded “Who art thou?”. Accurate rules of grammar aren’t immutable. Inaccurate rules of grammar, on the other hand, well, you can set them in stone, if you want…
We’re not talking about a dialect, though. Unless informed otherwise, you have to assume that a grammar or syntax question involves the general rules of English. The OP didn’t suggest that everyone, or even anyone, he knows does it that way; he just said that he did.
I’m not saying that there are immutable rules of English, but you have to attempt to enforce some sort of code, or you won’t understand anyone in the next country or state.
Also, your example isn’t the same. Using entirely new words or constructions is fine, because there’s no ambiguity as to what you mean. Using existing ones in a new way is a problem, because then your audience doesn’t know which “definition” you’re using.
We’re not? What are we talking about? (This isn’t pedanticism about a distinction between “dialect” and “lects in general”, is it?) I assume this minority of speakers speaks that way because they all happen to form a speech community wherein their speech patterns are standard. That’s generally how it would work; people pick up their way of speaking from their peers.
What do you mean by this? Clearly, different people speak English differently; some rules have wide applicability, some have narrower applicability. When presented with a question about English grammar or syntax, the best response takes all this information into account.
Do you doubt that the reason he does is because he has picked it up from the people around him?
Nobody has to enforce some sort of code; people do it themselves. People go around talking pretty much the same way the people around them talk, thereby maintaining enough consistency to understand each other in a coherent language. In your example, the people who do say “Who is you?” presumably find this construction as perfectly natural and comfortable to them as anyone else with their native manner of speech. I don’t begrudge the Frenchman his French; the way he speaks is not familiar to me and I have difficulty following it, but I accept that it’s perfectly reasonable that people from different places are used to different manners of speech. Why would this situation be any different?
But saying “Who are you?” or “You forgot your wallet” to one person is a new use of an old word. The word “you” was once only used as the second-person plural objective pronoun; singular and nominative uses of “you” were once just as new as your example of “Who is you?” is meant to be.