I'm glad you already solved it.

I was going to recommend keeping track of what's on your "clipboard" (or whatever Vista calls it). Windows 98 had the "clipboard viewer"; Windows XP's "clipbook viewer" did exactly the same thing; and I'd hope Microsoft would've kept up the tradition in Vista, 7, and whatever might be next.

If you thought you'd copied something but the clipboard viewer said you hadn't, you'd know the problem had to be with the Copy function. If the clipboard viewer showed you had copied it successfully but nothing pasted, the problem would have to be at the Paste end instead.