[Jimbuna]

Yes, certainly odd and something I've never come across or heard of until now.

In your second PM you state your friend hasn't set up his router.....my understanding is the router only has control over connectivity and access.

If the game is loading and playable for a period of time prior to a crash that would suggest both your installations are identical at startup but later on when the game calls upon further information one of you don't have what is being called for.

I'd suggest trying a basic mission from stock and if all goes well, add a unit at a time.

Slow and time consuming I know but the only way to identify what is causing the mission to crash.