Here's how I'd write the code... dunno if the tables and column names are correct because you didn't list the CREATE TABLE statement for any of the tables...
Code:
CREATE PROCEDURE dbo.InsertTiming
@Timing NVARCHAR(255)
AS
SET NOCOUNT ON
IF EXISTS (SELECT S_Time FROM dbo.Timing WHERE S_Time = @Timing)
BEGIN --Alert the operator if the timing already exists
RAISERROR(N'Timing %s already assigned',10,1,@Timing)
END
ELSE
BEGIN --Timing does not exist... insert new timing value
INSERT INTO dbo.timing(S_Test) VALUES (@Timing)
END
--Jeff Moden