Occasional dropped frames from 8mm tape capture

I'm using a Sony Digital 8 Camcorder TRV480 and WinDV to capture a bunch of old 8mm tapes. The problem I'm having is that on a 2hr tape, WinDV will report some dropped frames. It varies depending on the tape, but usually between 10-20 dropped frames.

Is this a problem with the timebase of the tape? or is this a hard drive issue? What is the best way of diagnosing this?

Thanks