128789 phpbb database error

I'm merging a database for phpbb, but keep getting the following error which I need resolving. I know the script to merge the database works as I've used it twice before successfully. However, their seems to be a conflict this time. The error is: SQL Error : 1062 Duplicate entry '0' for key 1 My forum is modded. I'm sure this is an easy job for someone who knows their way around mysql or phpbb.