This might happen if you have fed WibTeX with entries that do not match BibTeX standards. Please use a format like:

FirstName1 LastName1 and Firstname2 Lastname2 and Firstname3 Lastname3...

The key word "and" is crucial for WibTeX to format the author names properly. More than one first names are recognized, as well as additions like "van", "de" etc. Refer to the help pages for more details.