I may have an idea about the problem: my forum is on a subdomain, which is hosted on an external server of the main domain name.
I'm currently checking that with the external server admin.
But I wanted to know: is it possible to run the gallery on a different server than the forum (for performances and storage reasons too).
Currently, it's on
http://forums.polyloop.net/gallery2/ (which is on the external server where is the forum)
And I want to put it on
http://gallery.polyloop.net which is only a subdomain of my own server.
Because of the
vb integration, I think it's impossible, but I hope i'm wrong

Thanks!