I get this all the time. I have only recently started with C4D and i'm gettting this problem more that I should. At first i thought it was down to a crash but i've had it in all sorts of ways, with crash, no crash, files straight from a learning site, etc....MAXON do help and repair the file for you but i can't be depending on them to fix my files all the time. This problem strangely spreads to other files within the same folder. I've also had it on a Mac and on my brand new PC with RedShift.
I've been able to recover the file opening R21 a couple of times but some other times, this syste