Try this..
CREATE PROCEDURE [Catalog.JoinCourse]
@Return_Code INT OUTPUT,
@idSite INT,
@idCatalog INT,
@idCourse INT
AS
Begin
SET NOCOUNT ON
IF (SELECT COUNT(1) FROM tblCatalog WHERE idCatalog = @idCatalog AND idSite = @idSite ) <> 1
Begin
SET @Return_Code = 1
End
Else
Begin
INSERT INTO tblCourseToCatalogLink (idCourse, idCatalog)
SELECT c.idCourse,cl.idCatalog FROM tblCourse c
INNER JOIN tblCatalog cl ON c.idSite = cl.idSite
Set @Return_Code = 0
End
Return
End
Or
CREATE PROCEDURE [Catalog.JoinCourse]
@idSite INT,
@idCatalog INT,
@idCourse INT
AS
Begin
SET NOCOUNT ON
IF (SELECT COUNT(1) FROM tblCatalog WHERE idCatalog = @idCatalog AND idSite = @idSite ) <> 1
Begin
Return 1
End
Else
Begin
INSERT INTO tblCourseToCatalogLink (idCourse, idCatalog)
SELECT c.idCourse,cl.idCatalog FROM tblCourse c
INNER JOIN tblCatalog cl ON c.idSite = cl.idSite
Set @Return_Code = 0
Return 0
End
End