Google Desk Top - can't search mapped network drive

Well, the subject of this post says it all, pretty much.

But here’s some more info about the problem.
The google desk top preferences page tells me the following about the network drive I asked it to index.

Unknown error trying to access files during crawling

I looked on the google desk top help forums and lots of people seem to have asked this and got no answer.

So what about the teeming multitudes? Anyone got an answer for me?

Thanks in advance.