Very unusual. That type of freeze is extremely rare on OSX…probably indicates the problem is in hardware.
Offhand, I would say this is drive related..but its hard to say. Can you try different FW cables? Could also be your internal boot drive freezing…A physical problem, not a directory issue, that DW wont fix. When virtual memory accesses the bad sector, you freeze.
Bad RAM is also a possibility, but you have apparently been working for a while without problems, so that is probably not it.