WordPress MU

Hello everyone, I have some login problems on a new install of MU1.51, When using IE7, the new site based on MU1.51 redirects every login attempt to:

http://aa.bb/wp-login.php?redirect_to=%2Fwp-admin%2F

but it works fine in firefox and safari. In the same server another 2 wpmu sites based on MU1.3 have no problem at all. I don't know if it is caused by the uncommon tld of that domain.

I've enabled the cookie but it doesn't help. I've searched a lot and it seems that many have reported this but there's no consensus on solution.

I have this problem also, with mu 1.51

the same error seems to come up with whatever browser I use (IE, Firefox etc) There doesn't seem to be any clear resolution to this in the forums.

I think it's related with the domain suffix. Saying, I got this problem if I choose url "aa.bb" as the main domain, but the domain "cc.aa.bb" works fine. Is it possible to know your site address?