Game hangs

[armstp]

I have played through the full campaign as the Germans twice without problem, but I cannot get through a game as the Allies without the game hanging and being unable to continue. I have started three times as the allies and this has happened each time during the stage at which the convoys are moving. By that stage I am well into the game and have had no problems until it suddenly hangs [November 1941, June 1942 and July 1942]. Going back and redoing the move makes no difference, it still hangs during the convoy phase. Is this some glitch which can be fixed or am I just stuck with not being able to play a full game as the Allies?