WMP11 causes limited connectivity

I have some movies on a file server. The file server is connected directly
to a Linksys router. Wireless are 2 computers connected, one XP SP2 and one
Vista Business.

When I play movies on the XP-computer in full screen, everything works fine.
When I try to do this on the Vista machine it works fine until I switc to
full screen. Then after a few seconds the connection is lost and the Vista
machine displays: limited connectivity.

I have disabled IP6, still the problem remains.

Any suggestions?