I have had Putty connecting via SSH to my Ubuntu 12.10 server for several months. Yesterday I began to get the following error every time I connect:
PuTTY X11 proxy: wrong authentication protocol attempted
I can do everything in the session except launch X Windows applications. To my knowledge nothing changed on the Windows side, and I did recently install @20 updates on the Ubuntu side during normal upgrade maintenance.
I use Xming as an X server on the Windows client. And as I said it was working just fine. I have ready dozens of Google results searching on this error and most seem to involve the error happening after an SSH connection while attempting to SU or SUDO to another account, but this is happening to my regular user connection.
I have tried deleting the .Xauthority file in my home directory, also various xauth add commands to try and get the correct "magic cookie" back into the .Xauthority file. Nothing has worked.