mysql Foreign key constraint is incorrectly formed error

`table1` is the parent table with a column `ID` and `table2` has a column `IDFromTable1`. Why when I put a FK on `IDFromTable1` to `ID` in `table1` do I get `Foreign key constraint is incorrectly formed error`? (I would like to delete the `table2` record if the `table1` record gets deleted.) ALTER TABLE `table2` ADD CONSTRAINT `FK1` FOREIGN KEY (`IDFromTable1`) REFERENCES `table1` (`ID`) ON UPDATE CASCADE ON DELETE CASCADE; Both tables' engines are InnoDB. Both colmnns are type `char`. `ID` is the primary key in `table1`.