This occurs any time the VSM cannot communicate with the VEM. Are you using L2 or L3 deployment? I resolved a lot of niggly issues once I moved to L3.
Does the VSM see the redundant VSM and all the VEMs as installed modules?
Here is a quick list of Drupal URL's everyone will find useful.
Login user form: http://<site name/address>/?q=user
Logout user: http://<site name/address>/?q=user/logout
Note: If ClenaURLs are configured the "?q=" will not appear. (e.g. Login user form would read: http://<site name>/user )