This is fresh install of CentOS v6 and Xen v4.1 on a new Dell server following the tutorial posted at: 
http://wiki.xensource.com/xenwiki/RHEL6Xen4Tutorial Every thing went just fine, yet virbr0 won't work and when I run brctl show I get the following error message: 
[root@pe1950 ~]# brctl show
bridge name     bridge id               STP enabled     interfaces
virbr0          /sys/class/net/virbr0/bridge: No such file or directory
/sys/class/net/virbr0/bridge: No such file or directory
/sys/class/net/virbr0/bridge: No such file or directory
/sys/class/net/virbr0/bridge: No such file or directory
/sys/class/net/virbr0/bridge: No such file or directory
/sys/class/net/virbr0/bridge: No such file or directory
/sys/class/net/virbr0/bridge: No such file or directory
/sys/class/net/virbr0/bridge: No such file or directory
/sys/class/net/virbr0/bridge: No such file or directory
/sys/class/net/virbr0/bridge: No such file or directory
/sys/class/net/virbr0/bridge: No such file or directory
/sys/class/net/virbr0/bridge: No such file or directory
8000.000000000000       yes 
FYI, /sys/class/net/virbr0/bridge is there, it is not missing as the system claims. 
I read all threads about this problem, but none gave any solutions. Please help. Thank you