Is this a normal error that can be caused by a disk drive malfunction, or will my disk need to be re-written? I've never had any issue with any other disks except an unlicensed Hacker disk that sometimes gave Error #4: Disk card not authenticated (game maker ID).
The disk that is giving me probs is an official Kaette Kita Mario Bros. It works fine on side A, but always gives error# 23 when I need to switch to side B.
If it's just one disk and only one side, it's most likely physical damage of the side. Maybe rewriting will fix it.
It's probably a dirty spot on the disk surface--try cleaning it with a q-tip with a tiny amount of rubbing alcohol on it. Physical damage usually ruins the disk and it can't be rewritten.
Must be the disk. I moved the spindle around and cleaned any small area that looked questionable. After that didn't work, I used a super soft polishing cloth lightly soaked in rubbing alcohol and gave it a spin cleaning but still no luck.
Very stupid question, but if I'm holding a disk in my hand and I see that side A is stamped on it, the "side A" data is actually on the lower side marked side B and vice-versa, correct?
Yep, if Side B is giving you problems, clean Side A since that's the side that makes contact with the read head. I was going to add that to my response, but it seemed obvious. :)