access problem while running elgg in a frame with URL forwarding

Hi there,

to forward a different URL to my elgg-system i used the URL-forwarding-type "frame".
Now i can see this forwarded domainname in the adressbar - all the time. That`s perfect.

But now the problem is, that i can`t login in this framing version of URL-forwarding.
I can fill out the login-form, press enter and see the same reloaded page as a guest before.

Maybe it`s not an elgg specific problem, but rather a server configuration problem.

Does anybody have an idea about a solution?

PS: i use the IE 7