MTU settings on xbox live?

ok so me my neighbor has internet and i have the new xbox live wifi adapter so he lets me use his internet.....but the thing is.....it sometimees lets me connect but most of the time it says something about the mtu settings on the last steps to connection.....and when i do connect after about a hour it disconnects me so whats the problem???? o and he plays on the playstation network (psn) and i was wondering if that could have something to do with it?