I just ran into a user having similar problems, as a matter of fact he could not upload...
The problem was, the cookies were set to the www.domain
he had a .htacces redirect, redirecting all domain.com to www.domain.com
he had set the gallery url to domain.com instead of www.domain.com
Result he was unable to post in vbgallery, (either images or comments) because as the domain got redirected, it did not have the $_POST info attached to it...
FIX: if you have such a redirect, make sure that the gallery url is set to www.domain.com