Mark, we released Microstudio 2.400 in January. You should have received four emails from our store when you purchased Karaoke Suite 4. Find the Microstudio one and click its download link. It will say mstudio2315.exe but it will deliver the 2.400 version now.
This has a lot of upgrades, and one of the bug fixes is a problem that existed in 2.315 that would make it not write more than 2 discs before causing a problem. That may also be what you are experiencing.
Jaddams is right in his assesment also, your drive is "very old" today and may be part of the problem. I agree with Jon's suggestions!
