During compiling literature using BibTeX I've got the following message in the log file:
This is pdfTeX, Version 3.1415926-1.40.10 (MiKTeX 2.8)
(preloaded format=pdftex 010.12.7) 7 DEC 2010 00:33 entering extended mode
Missing character: There is no ę in font cmr10!
What should I do to fix this problem?
Probably the encoding of your bib file is utf-8 or some other encoding that BibTeX can not handle. BibTeX itself does only handle us-ascii properly, as far as I know, although it works fine unless no problematic characters occur. But without a working minimal example, your problem will be difficult to solve.
You need to replace instances of that character in your bibtex file with: \k{e} and make sure that you have \usepackage[T1]{fontenc} in your preamble (in your main document). For information on other accents and how to do them in LaTeX see here.
An alternative is to use biblatex and biber instead of bibtex as these tools can deal with more unusual characters directly...
