Network: Guest can't see Host

[kmma]

I have a Ubuntu as guset on a Win 7 Host. Network is bridged. IP of host is 192.168.1.25, IP of guest is 192,.168.1.24.
From host to guest a "ping 192.168.1.24" works (host can see guest), but in the other direction "ping 192.168.1.25" does not work (guest can't see host), but all other IPs work, I have access to internet and all other computers in my subnet, only the host is invisible.

Any ideas?

Regards Klaus