Roland Giesler | 1 Jul 23:36 2013

Failure negotiating the session in stage '7'. Wrong version or invalid session authentication cookie.

This error is most annoying to say the least, since no-where on the
internet is an explaination of the cause nor the fix for it.  Some
people seem to have managed to get past it by luck.

This is an Ubuntu 12.04 64bit server that had nxserver install.  One
day (probably after some update, but it was too long ago to undo of
trace now) the nxclient just stopped working.

I left it after many futile attempt to fix it.  I have completely
removed (purged) openssh-server and nxserver, nxnode and nxclient.
Numerous times, apart from creating keys manually and more.

So I though, let me switch to X2Go.  And lo and behold, I get the same error.

Strangely enough though, I can connect perfect to the server via SSH every time.

What causes this and how does one fix this please?