try reverting the templates changed one by one. After each reverted, try to access the problem page again.
If it's just a clean install from two days ago, then you can reinstall VB and forget all the hassles. But you need to re-configure your modifications.
You said you paid the firm money for the license and the site. Did you download the script directly from vbulletin.com members area or the script provided by the firm?
If it's provided by the firm, then those scripts may have been tampered.