References gone

The last time I was working through the bibliography of my document I had to discover that there were a few entries (3 or 4) that were no longer available in my library. As I would not delete my own references, could there be another possible reason or explanation for references that are suddenly no longer in the library? Where could they have gone lost or what could I have possibly done wrong?

Thanks in advance for your help!

Gremlins?  I can’t honestly think of any other explanation. Version of Endnote?

Maybe, don’t know…

It happened to a colleague of mine (who is using EndNote X2) and my task as his student assistant was to browse the Internet for a possible reason why this could have happened. But if you haven’t come across this problem so far … Thanks nonetheless for your reply.

maybe you removed some duplicates and now word is looking at an entry which was removed?