The row value(s) updated or deleted either do not make the row unique or they alter multiple rows (2 rows).
Put SET NOCOUNT ON as following:-
Create TRIGGER [dbo].[OBIEE_USERSTRI_DEL] ON
[dbo].[WC_OBIEE_USERS] FOR
DELETE AS
SET
NOCOUNT ON BEGIN
DECLARE
@USERNAME1 VARCHAR(100) DECLARE
@GROUPNAME1 VARCHAR(2000) SELECT
@USERNAME1 =USERNAME,@GROUPNAME1=GROUPNAME FROM Deleted insert
into WC_OBIEE_AUDIT(USERNAME,GROUPNAME,USERID,DATEUPD,WORKSTN,[ACTION]) select
@USERNAME1,@GROUPNAME1,SYSTEM_USER,getdate(),host_name() ,'Delete' END