From: United Kingdom
I was using a CRW6416S until I upgraded a few hours ago to a CRW3200S because of similar problems.
My drive was manufactured in June 1999/bought in July 1999 and was running the latest firmware version 1.0d (think the drive shipped with 1.0b), however I began to suffer from this problem when I started using Win2k Pro, the only way I could read the CD that I had burned in the drive was to reboot, after a while I went back to using Win98se and for a time it was okay, then it started happening again, I don't recall upgrading any software at the time.
Another problem which happened over time was the recognition of CD-RW media after formating with this drive. Which when I did the drive did not pickup the media at all, the On/Disc LED stayed solid amber when CD-RW media was inserted, the only way I could reclam the media was to do a full format on my CRW2260S which the CRW6416S was ment to replace, then the disc could be read and writen on my CRW6416S.
Also sometime when using cheap unbranded media like Prodisc Phthalocyanine based discs, the drive could read the media but would show a CD Audio track along with some cheap no-name IDE CD-Rom drives, my Plextor 40TSi would read them okay with a little bit of coaxing.
So to sum it up, I think your drive could be on it's way out.