Hi everyone,here's the problem:

Computers in Lan A can not access anything in Lan B but from Lan B everything is ok.i guess the problem is with Xen.because with same conf i have tested and have no problem on another phsyichal maschine(openvpn server).

Lan A:
Ubuntu bridged
Openvpn client
Lan B:
Xen guest bridged (Debian squeeze)
Openvpn server