If you are using VSA r9.1 - newer the VSA has an integrated AuthAnvil legacy TAP Module. This module has an XML file that can become corrupted. If this occurs simply download the attached file to replace the one on server.
File location: C:\Kaseya\vsaPres\AppMetaData\Applications\1Home\ModulesAuthAnvil.XML
Note: We do not recommend renaming the original as a backup in the same folder. This has been known to cause errors in the modules when VSA is accessed.