License Class Not Found

[DaveSch]

I don't know why random errors keep popping up every few months, but suddenly I am getting the following error when trying to access anything to do with the sitebuilder (including the login page):

Internal SiteBuilder error.
File: /usr/local/sitebuilder/include/SB/Environment.php; Line: 94
Message: License class not found.; Code: 0

Does anyone know what might be the cause of this?