Hello, Julien pointed me to the right place:
> You also need to use a natbib-compatible bibliography style. You select this by clicking on your "BibTeX Generated Bibliography" in your LyX document and selecting e.g. plainnat Actually, I would have chosen plainnat as in some older documents, had the option been there. But all I can chose from is "plain". I think this once again is the "network drives in Windows" problem (http://www.mail-archive.com/lyx-users@lists.lyx.org/msg87682.html) as I am still using the same setup (Windows XP, network user with limited rights, LyX installed by a local admin). I am now working on another computer (Windows 7, local admin installed and uses LyX) and the same document compiles fine after I chose "plainnat" from the many options offered. Still no solution for the other computer, but at least I now know some background of the problem. Matthias
