File Transfer Error on New 6400 when Downgrading to 3.3.33

I have a 6400, TGXL, and PGXL all in a rack and on the same network. I run 3.3.33 which works great. I have not upgraded just yet. If it ain't broke, don't fix it.

I just bought a new 6400 as a backup and wanted to bench-test it and put it away. My goal is to set it up as a duplicate in every way to the current 6400.

When I connected it to power and the LAN, SmartSDR found it just fine and as expected, indicated the new radio needs to be downgraded to my current version 3.3.33 as the radio presumably came loaded with 3.5.8.

I started the process and the yellow bar started moving to the right, and then a "File Transfer Error" popped up. I clicked it and started over, the yellow bar kept moving to the right and then the same error popped up. I kept doing this and each time the yellow bar made more progress, but I gave up as I didn't want to corrupt the new radio. Also tried rebooting the new radio to see if it would complete the downgrade without the error. No such luck.

I realize a solution would be to upgrade to the version the new radio came with but as I said, 3.3.33 is working almost perfectly for me.

Any suggestions as to why this error is popping up?