X11 connection uses different authentication protocol.
X11 connection rejected because of wrong authentication.
..
Unable to open display remoteserver.com:123.0 Disconnected. Protocol error (Too many authentication failures for user_a)

Putty X11 proxy: wrong authorisation protocol attemptedUnable to open display remoteserver.com:123.0 ... Disconnected: Protocol error (Too many authentication failures for user_a)