Dumb workaround but works for me
Im running MPB core 2 duo, 2 GB RAM, parallels RC3 5170, bootcamp.
From time to time, it does not boot saying Unable to Open Boot Camp Image.
I saw that somtimes, just editing the VM properties, i.e. making a small change to allocated memory just make it.
I do not have a clue why is that, but usually when it refuses to boot, I do that and voila.
Just for the record, Im running MS SQL and a few apps that I do not like their current Mac versions i.e. Yahoo IM.
Im making heavy use of MS SQL server while doing development work and everything looks great. No unexpected quits, no nothing.