I have the exact same DVD recorder (DMR-EH50, I believe the S is for Silver, right?). The first unit was acting up, I think; it lost the TV Guide twice in the first week, and I recorded a few DVD-Rs that I could not play in my older Panasonic DVD player (which is supposed to play DVD-Rs). They played fine in my PowerBook though.
Anyway, the fact that it lost the TV Guide and I had to wait another 24 hours to download it again (24 hours with the unit OFF) made me exchange it. The new unit is flawless. Not a single time it lost the TV Guide, I had it since Thanksgiving. Also, the DVD-Rs play fine in the other Panasonic DVD player.
I usually record stuff from PBS, NBC and I think the wife has a show on ABC she records. I could try to help you, I will try to record some show on CBS and see if it works. PM with details, I will set it up for tomorrow night. Are you on the East Coast??? and BTW, are you a Physicist???
another random thoughts: make sure there is enough space on the hard drive. have you tried to record to DVD RAM instead? have you changes the recording quality? have you changed the frequency (REGULARLY instead of ONCE).
Also, make sure the show is indeed in the SCHEDULED list and not in FAVORITES list, I believe that if in favorites, it merely reminds you, but it does not record it.
Anyway, PM with details and I'll help you.