This usually indicates a problem in the html that is used to construct the page. Things to check in offending page source (i.e. view the abstract book and then view the page source) include:
1. MsoNormal - a class that usually copies over from MS Word.
2. _mcePaste - an id that copies over from MS Word.
3. all occurences of <font> should be searched and removed.
When createing PDF, use Firefox 4 print preview and adobe acrobat as the output printer.