Hello, I try to delete a FK in the following way

ALTER TABLE ACTIVO DROP CONSTRAINT FK_ACTIVO_11

and get this error message:

This operation is not defined for system tables.
unsuccessful metadata update.
ERASE RDB$RELATION_CONSTRAINTS failed.
action cancelled by trigger (1) to preserve data integrity.
Cannot delete trigger used by a CHECK Constraint.

We are using FB1.5 SS on Linux.

Any idea what I have to do to delete this foreign key?

Thanks

Stefan