This is an issue with
vbSEO. Our product works fine with vbulletin 4. I beleive there is a setting in the
vbSEO admin panel to disable that product on specific directories. You dont do it in an htaccess like you did in previous
vbSEO versions but they should have more information on this. There application in a nutshell is preventing our VB40 variable from being defined.