Friendly error message for Unique Constraint

--UQ_dept_Uf_ILC_CostCodeType
IF NOT EXISTS (SELECT TOP 1 1 FROM ObjectMainMessages WHERE ObjectName = 'UQ_dept_Uf_ILC_CostCodeType' AND MessageType = 17)
    BEGIN
        DECLARE @NextMessageNo  int

        SELECT @NextMessageNo   = ISNULL(MAX(messageno),799999)
        FROM ApplicationMessages
        WHERE MessageNo BETWEEN 800000 AND 999999

        SET @NextMessageNo = @NextMessageNo + 1

        --add main message 100093 = The &1 entered already exists.
        EXEC AddObjectMainMessageSp 'UQ_dept_Uf_ILC_CostCodeType', 17, 100093, 16, 'Dept Cost Code Type UQ violation', 0

        --add the substitution text
        EXEC AddApplicationMessageSp @NextMessageNo, 'Cost Code Type', N'1033'

        --add substitution text to main message
        EXEC AddObjectBuildMessageSp 'UQ_dept_Uf_ILC_CostCodeType', 17, 1, @NextMessageNo
END