Update rows which match another table using Stored Procedure in SQL Server

Hi..

I have renew for my storeprocedure like this

ALTER PROCEDURE [dbo].[sp_shipment_assignment]
	@id int, 
	@end_date_time datetime, 
	@vehicle_id int, 
	@begin_date_time datetime,
	@origin_id int,
	@destination_id int
AS
BEGIN
	SET @begin_date_time = (select begin_date_time from shipment_assignment)
	SET @end_date_time   = (select end_date_time from shipment_assignment where end_date_time <> NULL)
	SELECT date_time from event_with_location where vehicle_id = @vehicle_id and date_time >= @begin_date_time
    WHILE EXISTS (select @end_date_time from event_with_location) AND @end_date_time <> 0 AND 
        BEGIN
            Update shipment_assignment set end_date_time=@end_date_time , active = 0
        END 
	SET NOCOUNT ON;

END

but its still error