Managed to get up and running again after some uninstall and re-installs.
I have made a new template, new server connection, new tables, lettings & sales, with information in lettings, but nothing works, still getting MM_ERROR: An undefined error has occurred.
When I click on lettings the Key Column has nothing in it, only the above error as a choice.
If I change to the sales table the options are there.
If I just ckick on Next with the lettings table selected a box comes up with "Please select a table that contains at least one column within it".
Do you think renaming the lettings tabe with do any good?