X11 connection rejected because of wrong authentication.

This is a less than completely useful error message; I got it when I 'ssh -X'ed to a Linux host form OSX and tried to 'sudo system-config-securitylevel'.  Here's the actual message

X11 connection rejected because of wrong authentication.
The application 'system-config-securitylevel.py' lost its connection to the display localhost:10.0;
most likely the X server was shut down or you killed/destroyed
the application.

A workaround is to do 'sudo xterm' and then 'mkxauth -m username' and then do the 'system-config-securitylevel'.
I don't have a clue as to why and don't have time to figure it out...

Update: a better approach is probably "sudo -- sh -c 'mkxauth -m beaty; command"

Another update: under debian "xauth merge /home/beaty/.Xauthority"