"unspecified error"

I am using the trial version of endnote x3 on a windows xp sp 3 machine, and my word processor is word 2003.

At present, I am uploading citations from a word document onto endnote. Upon filling out reference information, I switch to word to insert the citation into the document. I had no problem with the first 20 references. The 21st reference was also placed into endnote without a problem. When I tried to insert the 21st reference into the word document, however, I get the message box “unspecified error”. The only option I have is OK. When I click ok, the citation remains in temporary format {in these types of brackets}. At the same time, the bibliography disappeared and won’t generate anymore. 

I have been unable to find any information regarding why this has suddenly occured, or how to get rid of it (although perhaps I missed something on the forums).

I have inserted several more references, and some input as completed citations (in parathesis) but some are temporary {in brackets}.

Would anyone know why this might be the case? 

Thank you for your time