Debugging messages look ok, except for the exit status, but...
1. The authentication method gssapi-with-mic does not work and can be disabled, either by modifying the /etc/ssh/ssh_config or by passing the option in the command line:
scp -v -o "GSSAPIAuthentication=no" some_file user@host:
however, I don't think this is the problem.
2. The welcome message, as any other output coming from the initialization files (.bashrc or .profile) can trigger the scp failure. To test this, you can try to temporarily remove the welcome message from wherever is generated and retry the scp command.
3. The message
Sending file modes: C0664 0 nc
means you're copying an empty file, but maybe you're just testing. Anyway, scp permits 0 bytes transfers.
I am for the second point...