There are certain situations where you cannot combine two numerically adjacent tracks, I know, such as the case where one is stereo and one is in mono, but these two were recorded as one and had just been (mistakenly) divided a moment before!
I had recorded that track from a radio broadcast at the logical end of the MD at the time and then had moved the track, in its entirety before the mistaken track division, earlier in the TOC to alphabetize it by the artist's name. My accident occurred after I had moved the track; I don't know if that's relevant or not, because it still was a single recording, not the jumbled result of previous edits. Nor was it a case where I had divided it, moved the two parts separately, and then couldn't recombine them: I had moved the whole track as one piece before the mishap. I don't know if I could have recombined them if the accident had occurred before I moved the track.
Removing and reinserting the MD made no difference. Several times over the next few months I tried again with no better luck.
The day I got my MDS-JE500 one of the first things I tried was recombining those two pieces into the single track they should always have been; it worked on the first try. I rewrote the TOC and the MZ-R3 recognizes the fixed recording.
The write-enable tab is now carefully slid out of the way on that disc.
-David W. Tamkin (email@example.com)