What is "return code" for WAL send command

Hello

I have a master PG 8.1.11 sending WAL files to a cold-standby using rsync

For some reason it failed recently with "return codes 32512" and I couldn't find this num. as a valid rsync exit code

During the time that the error was going on I tried the rsync command manually and didn't error

Can someone tell me what kind if error is 32512

Thanks

Mr. Wu