I'd tried that ... after the remote locked up upon download, I pulled the batteries until it died, then replaced them; once the remote finished "booting" (the checkup sequence), I performed a MAIN+STOP reset back to MX defaults, then applied a "blank" file to the remote - the blank file completed download successfully. At this point I downloaded the actual config, which also completed download successfully.

It's upon subsequent attempts that the download continues to fail & remote locks up, now :(