[8.281][BUG][OPEN] IE8 and Webadmin

I have two Beta ASGs and an ACC3.0.

From my Client (Windows7 64bit) I try to connect to these Systems.
But only one(ASG) is answering with the loginpage. The others showing an "Webseite kann nicht angezeigt werden".
(When I try to ceonnect to Customer ASG everything is fine - 8.103 to 8.202 Systems)

When I use Firefox8 everything is working.

Any Ideas?

Sven