Our classifieds has no interaction on your forums so not sure why you have an error on your forum since your forum should not know classifieds is installed at all. We load the vb
header footer style around our application which shows in the classifieds directory. I would suspect a hack or mod issue if you installed a mod or something to vbulletin recently.
As far your next error thats a pretty common vbulletin installation mistake. On the last step of install you did not specify the correct vbulletin server path where asked. Number 2 on this FAQ should assist you. vBulletin Installation/Integration Common Issues and Resolutions.