Problem with Panasonic AG-1980 VCR
 

I'm having a problem with my Panasonic AG-1980 VCR. I'm trying to copy a vhs video with it, I'm using it as the recording VCR, and another VCR as the playback one. After about 2 hours, the AG-1980 stops the video, and rewinds itself. The video I'm copying is 6 hrs long. I've tried this twice, and it did it both times.

Why is it doing this, and how can I fix this?

I haven't checked the manual, but perhaps the "One Touch Recording" function is turned on? I'm also assuming that the AG-1980 is set to record at EP speed.

You may have mashed the OTR option (one touch recording), by hitting record twice.
Each press of OTR usually gives a 30-minute extension.

A 6-hour VHS-to-VHS is quite frankly going to look like crap.
The VCR did you a favor. I'd record a 6-hour video to 3-4 SP mode VHS tapes.