Answer: If you have multiple authors in your reference, make sure you have placed each author name on its own line. If you have not done so, be sure to enter a carriage return after each name. There should be no punctuation between each author as the Output Style will include this information:

Argus, Michele V.
Matthews, Edward K.

If you are still having problems, go to the Tools menu and choose "Define Term Lists". Highlight the "Authors" on this list. Make sure that no delimiters are selected below, as that will cause issues. Uncheck all delimiter boxes if they are checked, and then click ok.