To explain a bit further. There are 3 posts so far of people who's attach in conversations would not work. This was due to a modification that had added a column that xenforo 1.1 was to add, so because we uninstalled the attachment modification after upgrading it then removed a column that is required by 1.1.
- Check version currently being used
- Check what columns are to be added
- If any of them columns exist before upgrade, there is a problem so therefore error stating x column on x table has already been added to the database.
- Check on install of a modification if any SQL statement is inserting a column/table using xf naming convention.
- On finding, error and state as much