well the file in question references some other scene files and has some objects from scene files exported into it, but it is only this .mb file that has the problem.
other maya (.mb) files on my computer are fine, even an earlier version of the file in question is fine.
some information that might be useful: I was working on 2 different computers when creating the file, when at home i would work on it, save it, put it on a usb key and then transfer it to the computer in class, then save it, transfer it to the computer at home, etc etc. unfortunately i wasnt copying the whole project file over, just the .mb file. i heard that wasnt good procedure. but could it have caused this problem? i did it to other files too and they are still fine.