Computer software on my Z-3 scrambled - why?

I took a trip recently in my Beemer and it was working fine under both highway and back road conditions. We stopped for lunch and as we tried to leave the car cranked, but would not start. I removed the fuses, and even unhooked the battery and reset the security code. Nothing changed, the car cranked but never offered to start. We had it towwed to a dealership and they found that the software had scrambled. The security module and one other one were not communicating. The Tech reprogrammed the computer and everything is fine except now I don't trust my car. The service rep. said he had no idea what might have caused this other than a strong magnetic field. There were cars parked on both sides of mine and they had no problems starting up and leaving, so I don't think that is what happened. Any ideas?
Thanks