If you disable vbWiki does the 'session error' go away?
(To disable vbWiki simply comment the line added to LocalSettings.php)
We used to have the 'session error' back on version 0.7.4 several months ago.
If the error still happens when vbWiki is disabled then refer to this thread:
http://www.nuhit.com/forums/vbwiki/2...tegration.html.
If the error doesn't happen with vbWiki disabled, then we have to look into it and fix it...