I tried to remove vifname and vif-script but the problem remains. I think that the bridges are ok, but for some reason VM's hang when they try to connect their vifaces to them.

I'll try some different configurations of the physical ifaces (an vifaces also), maybe I'll be able to find out something. Also, I'll focus on the vTPM, since the following line shows up in the Xen log when the VM tries to bring up the iface connected to the second bridge:

[2011-11-18 09:27:16 xend 8213] DEBUG (DevController:160) Waiting for devices vtpm

Furthermore, it appears that sometimes the VM's manage to start regulary, I just can't figure out when & why :/

Tnx for your comments ..

Br, M.