Remote Desktop - Connection closes at login


I am running Windows 7 on my Laptop and Windows Vista on my desktop in the same wireless network. I want to connect from Vista(desktop) to win7(laptop) via Remote Desktop Connection. On the win7 system, the settings for rdc are all changed. On the vista system I use RDC 7.0. For connecting I type in the IP, username and password of my Administratorprofile, which is currently logged in at win7.
RDC connects, the Administrator at the laptop(win7) is loged off automatically, and loged in via RDC in the same moment. At vista, where RDC runs, I can see the Welcome screen. But then RDC loses the connection, and shuts down after several attempts to reconnect.
When I log in at the win7 system, I can see, that the connection to the wireless network was closed. That means, in the moment RDC logs into the win7 account, the wireless connection closes and RDC fails.

The funny thing: It already worked! Until I installed MS Office 2007 (and maybe some updates). I tried system restore to a point before the installation, but it won't restore, I dunno why. I tried to deinstall all updates and MS Office but that does not help out. I tried to reconfigure all energy options at the win7 system to prevent it from closing the connection. no success.
Can anyone help me?

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