What's the difference between the RV31 and RV31K? I assume the K is for color of the machine as the silver model is RV31S.

I have a RV31K.

I wanted to report a problem with certain VCDs. On a few VCDs towards the last 20 minutes of the disc, the frame rate drops and the video looks very jerky. I burn all of my VCDs at 4x, and use the same media for all discs. These VCDs play back perfectly on my pc.
Does anyone know what the problem could be? Anyway to fix it?

Also does anyone have a region unlock or macrovision disabler code for the RV31K? Will codes for the RV31 work on the 31K too?

Thanks!

Milan