[Koha-devel] koha 3.0.4 + cannot delete extra libraries with their names

Hi, i want to delete some extra libraries from my koha system. Then, i could delete three from GUI; Koha-> Administration-> Libraries & Groups. But, there are more two including default "My library". Then i went to mysql an tried to delete those two library names, which are as sub-branch; but, i cannot delete those. Error shows: * mysql + #1451 - Cannot delete or update a parent row: a foreign key constraint fails* -- Best, Zico