Raise Error

I am trying to raise a simple error in a trigger...But apart from my error it also displays two other errors. ORA - 6512 at line 10
and ORA 04088 : error during execution of trigger

My trigger code is

CREATE OR REPLACE TRIGGER CBS_OWNR.BATCHJOBS_TRIG_CHKGROUPNAME   BEFORE INSERT OR UPDATE OF TOGROUP ON
CBS_OWNR.BILLINGBATCH_BATCHJOBS
  FOR EACH ROW WHEN (NEW.TOgroup IS NOT NULL)

	DECLARE
		NUM_RECS NUMBER;
		FINAL_GROUP VARCHAR2(30);
		E_INVALID_GROUP EXCEPTION;
	BEGIN
		SELECT COUNT(*) INTO NUM_RECS FROM CBS_OWNR.BILLINGBATCH_EMAILGROUPS
WHERE GROUPNAME=:NEW.TOgroup;   --line 10
		IF NUM_RECS = 0 THEN

				:NEW.TOgroup:=NULL;
				RAISE_APPLICATION_ERROR(-20901, 'Group Does not Exist');
		END IF;

	END;