Was it a type of attachment you’ve never gotten before, such as an Excel document? (xls)
Was it a Word document with form fields in it? (hidden or not)
Was it a Powerpoint document?
Oddly enough, Microsoft’s own programs tend to be treated most cautiously by Microsoft (I’ve run into problems sending things to Outlook users) and can also do the most damage to Microsoft machines (not inherently - I mean it’s easy to send malicious code using those file formats. Your boss was not doing that but Hotmail was being better safe than sorry).
Anything I might suggest would just be a guess…I’m a functional illiterate when computers are involved. In my case, I reviewed my e-mail settings to see if anything had changed, and added the sender’s e-mail address to my “safe” list. Another possibility might have been the size of the file, but that gets into the realm of guessing, based on my limited experience.
First of all, yes, a little while ago (but, been a few months) MS forced an upgrade to Hotmail Live on all subscribers. As with so many of their upgrades, this one is buggy, unstable and a PITA. One nuisance is this security feature, whereby attachments, scripts and other such in messages from folks not on your safe list (which includes contacts) are blocked. I’ve never seen a block, though, where I couldn’t unblock for that message. Also, adding the sender to your safe list or contacts should solve the problem.
Mine has been doing that pretty much forever - it does it because a lot of spam contains linked images that are uniquely named so that when you open the message and your machine requests the image from the web server, the sender of the email knows your account is alive and knows it’s worth sending you more crap (or adding you to a list of ‘verified’ emails that can be sold to other spammers).
There’s a button or link to open the message showing full content - it’s not a big deal.