Multiplayer problems

I have flight simulator x that I have just reinstalled and working fine. The multiplayer was working fine the other night this was with my home pc directly connected to my virgin router and both my sons computers directly connected.

Last night I hosted a sever on the multiplayer through FSX and both my sons logged onto it but with in one minute both there screens freeze and a box opens up say the game have to shut down sorry for the inconvenience. My son tried hosting a sever then when we both connected to his sever I then got the screen freeze and the message the game needs to shut down sorry for the inconvenience