Please go to the Elgg wiki (click on Docs on the site nav) and do a search on misconfigured plugin. 

Thanks! I actually went ahead and downloaded the latest version through subversion and that took care of the problem.  I believe the index.php file was missing.

@Floyd - no, index.php is included in the zip file. Misconfigured plugin is explain in the wiki and it has nothing to do with any index.php file.