Edubuntu 14.04 + upgrade, can't login

[Peter Jones Bus]

Hi

We have just installed the above on a dual boot HP G.250 laptop.  All was well until Edubuntu requested we upgrade from 14.04.  The machine downloaded a lot of stuff and now we get a “failed to start session” at the login page.

This error is described on the ubuntu page, we have tried the fixes proposed there but nothing seems to work.

HELP!

Thanks in advance
Pete & Luca