Okay, a couple things here... First of all, to answer your questions about my problem:
How long is the entire path plus the filename? I've run into odd problems in the past when the ENTIRE path and filename exceeds 255 characters, which can happen more easily than you'd think...
The entire filename (including the path) is 98 characters long.
Make sure your using the Latest version Of MC 11.1
The problem came up again today and I'm using 11.1.167, which is the second-latest version (Thursday's build).
Second thing, I want to point out that there are two bugs here. First, MC is incorrectly claiming that my external drive doesn't support long filenames. If it's the entire pathname that it is complaining about, then why is it forcing me to rename just the filename portion to 8.3 characters? But regardless, I'm certain my external drive can support a 98-character pathname including a 25-character filename.
And the second bug is that after MC forces me to rename the file, and successfully moves the file to the new location (with the shortened name), it does not update the Filename field in the library, which means that it loses the file.
The first bug is annoying, and the second one is crippling. I'd love to see the second bug fixed immediately, and the first one fixed real soon now.
Thanks!
Solomon