WinSCP 5.5.3 (build 4214) CentOS GNU/Linux 2.6.32-642.15.1.el6.x86_64 Login configuration: SCP protocol, port 22, everything else is default.
The error: Connection has been unexpectedly closed. Server sent command exit status 254. Error skipping startup message. Your shell is probably incompatible with the application (BASH is recommended).
getent on the remote Unix server reports that my login shell is indeed /bin/bash, which does exist with perms 755.
I've looked all over the WinSCP help forum for a solution. Nothing there makes any sense - in most cases, I can't even parse the replies to the person having the error.
I tried looking up "scp server status 254", and found a tip here to turn off PAM (in /etc/ssh/sshd_config, set "UsePAM" to "no"). Same error.
What more can I do to diagnose this problem?