I have a MySQL table where the Primary Key (int) was set by the software to be equal to the Primary Key (auto incremented) of the main table. Because of a change in design I now need the field to auto increment. When I tried to ALTER TABLE it came back with the following:-

```
ERROR 1062: ALTER TABLE causes auto_increment resequencing, resulting in duplicate entry '1' for key 'PRIMARY'
SQL Statement:
ALTER TABLE `Clinic`.`ClientSupplementary` CHANGE COLUMN `idClientSupplementary` `idClientSupplementary` INT(11) NOT NULL AUTO_INCREMENT

ERROR: Error when running failback script. Details follow.

ERROR 1050: Table 'ClientSupplementary' already exists

```

This has me totally puzzled as '1' is definitely unique as are all the other Primary Key values. Where should I be looking?