Thanks, that useful. I’m away for the weekend so will get back onto this Monday morning (its not an important site so I have just taken it down by redirecting the url). The database seems to have been partially updated to the new prefix – the core tables have the old prefix but all the additional tables (the plugin tables) have the new one. I guess this is the problem. Maybe I’ll just revert to a backup of the database.
Thanks for your your help, have a good weekend. :)