Help needed with pid error (Solved)

Hi Mark,
When I switched on this evening I got an error, on the top left of the desktop the box says
Error No session for pid 1406 and when I click ok it says,
Temporary Guest Session, All data created during this guest session will be deleted when you log out, and settings will be reset to defaults. Please save files onto some external device e.g. to a USB stick, if you would like to access them again later.
I have then clicked the ok then from the menu logout then shutdown.
Any ideas ?
EDIT I have just switched on again and I am presented with a guest session log in ?

You could try:
At login screen, press Ctrl+Alt+F1 to switch to console mode

Use your username and password to login

Then enter the following commands:

sudo mv .Xauthority Xauthority.old


sudo shutdown -r now

Then boot up and try to login as normal

Thanks Sezo,
I carried out your instructions and all is ok now.
After I did the sudo shutdown -r now, the machine restarted itself and gave me the guest login, I clicked the little down arrow and logged in as myself as usual and it seems ok.
Thanks for the help.

Glad it worked for you.
If you are happy with the solution perhaps you could mark it as SOLVED