Xlib: PuTTY X11 proxy: wrong authentication protocol attempted

I had this weird error when trying to start an X11 application.

oracle@dbserver:~ $ xclock
xlib: connection to “localhost:12.0” refused by server
Xlib: PuTTY X11 proxy: wrong authentication protocol attempted
Error: Can’t open display: localhost:12.0

Next you try the steps described here to transfer the authorization to the other account. But if you follow the steps and it simply doesnt work, check the filesystem where the home directory is.

oracle@dbserver:~ $ df -h .
Filesystem            Size  Used Avail Use% Mounted on
9.9G  9.4G  128K 100% /home

In this particular machine, I was having the authentication protocol error because the OS couldn’t update the .Xauthority file in the home directory.