Scarey stuff, but I am thinking along the lines of Stephen, having experienced a cross reference of files in another Windows program (Word). It happened on a drive I do a lot of work on, and I think it powered down and up once following a power glitch, so there was a chance of cross-linked files. I reformatted the disk and checked for errors, installed a UPS and have had no problems since. All that to say have you had any odd issues with the drive the project file is stored on?