Am still waiting for tech support. In the meantime I made a change to the database as per this thread showthread.php?t=11496. As I still couldn't log into the backend I commented out line 6 in Admin/index.php. Tried to login and got a different error message but all the menu items were available so I clicked settings and I was there. I then made a change to the administrator password and guess what it saved. It's not a glamorous hack but it means I can now get in and start customising things till the techies sort it out.