When trying to delete an agent procedure, you receive a message that the procedure cannot be deleted as it is used by another procedure (the procedure is named in the message).
Kaseya allows a procedure to call other procedures. If the parent procedure is still on the system, then child procedures (those which the parent uses), cannot be deleted, as this would cause issues.
WORKAROUND / RESOLUTION
Locate the parent procedure (named in the message dialogue) and either delete that, or modify the parent so that it is no longer calling the child procedure (the one that you are trying to delete)