ah the vb
support site has info on how to disable there hook system but this should help http://www.photopost.com/forum/1303154-post2.html
Your issue is definately related to how you installed plugins so disable plugins then go in and uninstall the photopost pro plugin and then reread the instructions on that plugin and you can redo things and make sure to reinstall it. I would suspect maybe you did not generate the plugin correctly or have permissions right.
remember after getting vbulletin hack up and removing the pro plugin then you need to remove the line from your vb
config file so your plugins will be active again and you can verify you have reinstalled plugins correctly. If you do things should be active and your site should look like the example I provided.