[CentOS-virt] No console from VM Manager since 5.1

Since I updated my CentOS 5.0 host machine to 5.1 I cannot open a console from the VM Manager to a guest. Before 5.1 it opened a VM window that looks close to the VMWare window and displays the console in it, so that I can login to the console. Now I get a "pre-window" that shows a "password" textbox, a Login button and a checkbox for "Save this password in your keyring". What is this? What password am I supposed to enter? Entering the root password (of host or guest) does not work. Once I press the Login button it just hangs and when I try to close it I get a warning that it hangs and when I kill it this way the VM console and the VM Manager are destroyed. I can login via "xm console".

Kai