... there is no reason to UEE for vorbis unless your using the GT3b1 builds that are tuned especially for -q 5 and above.
Sorry if my initial message was misleading, but this is exactly what I wanted to do.
I ran across another weird symptom ... that is, as an experiment, I tried converting some 320kbps MP3 straight over to Ogg, and came across the same "failure to import" errors, the resulting Ogg being a good file, but untagged and not imported. So, I first converted them to WAV, and then from WAV to Ogg. The action worked for many conversions, including tagging and importing ... but then started to fail after about 6 tracks.
I realize "sometimes works, sometimes not" is a lousy amount of info to hand over to developers. Let me know if I can provide any more info (... btw, I tried moving the files and temp area to a part of the drive, so that MC wouldn't have to deal with long paths, but that didn't work either).
I hope J River will explore this issue with respect to MC9.1.
Happy Holidays!!!