CLI FTP Transfer error number 106 for PTP820c

I’m trying to automate the firmware upgrades to our PTP 820c radios through the CLI. I’ve tested it in the lab successfully, but when I try to execute the firmware download on the production network, I end up receiving the following error:

root>platform software download version protocol ftp
error number 106: CLI command execution failed

I have the ftp server information entered correctly, but I’m getting hung up here. In fact, if you look at the logs on the ftp server, the radio doesn’t even try to connect to it ever.

I can’t find anything on what error number 106 might be. Is there a resource that explains the errors and how to work around them?