DVR stops recording after ~ 2weeks

I'm new to this DVR stuff but a surveillance system we have setup at a small business of ours works perfectly fine for 2 weeks or so but at that point stops recording. A quick reset seems to get it up and running again though. It doesn't seem to be that the harddrive is full because looking at the status, it constantly clears up space as it records as it should. Anyone know why it's doing this? Thanks.