For some reason my B-25 crashes to desktop as well, but it does it at the end of the flight, when I hit Esc to return to the top level screen. It's done it since day 1, and it's the only plane in my fleet that does it. It's more of an annoyance than a serious problem, since I do get to complete the flight.
I'm running FSX Gold on a quadcore i5 at 3.0 GHz, 8GB RAM, Win7 Ultimate 64-bit, currently using a Radeon 6670 but it was happening while I was still running the onboard Intel graphics chip too. The MAAM packages were among the first addons I installed in FSX, if not the first; I bought FSX specifically to fly the R4D, the B-25 and the TBM.