Error if somebody upload Thumbnails

[snakes1100]

Is safe_mode on?

admincp --> maintenance --> view php info

Look for safe_mode on/off, let us know what its set to

If its on, use the option in the admincp to set a directory to allow uploads in a safe manner to not harm the server as its a vhost.

admincp --> vbulletin options --> Server Settings and Optimization Options
Safe Mode Upload Enabled <-- set to yes
Safe Mode Temporary Directory /temp <-- this is relative to your public_html/root folder.

Ie...
http://www.mydomain.com/forum/temp and chmod the new temp folder to 777