Error On Procedure

Hi frenz:
I have created the following procedure.While running the procedure i met the follwoing error

Error:

" Msg 245, Level 16, State 1, Procedure Sp_Aft_GetAllCategory, Line 15
Syntax error converting the varchar value 'Select PCatName,PCatDesc,PCatId from Aft_Tbl_ProductCategory
Where ModuleId= ' to a column of data type int.".Can any one clear the error.


My Procedure:


USE [AftronProducts]
GO
/****** Object: StoredProcedure [dbo].[Sp_Aft_GetAllCategory] Script Date: 05/26/2008 19:46:05 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
-- Author:
-- Create date:
-- Description:
-- =============================================
ALTER PROCEDURE [dbo].[Sp_Aft_GetAllCategory] (@ModuleId as int,@ColumnName as varchar(50),@SortOrder as varchar(50))
-- Add the parameters for the stored procedure here

AS
BEGIN
declare @sql as varchar(1000)
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
set @sql='Select PCatName,PCatDesc,PCatId from Aft_Tbl_ProductCategory
Where ModuleId= '+ @ModuleId +'
order by '+ @ColumnName +' '+ @SortOrder + ' '
exec(@sql)
print @sql


END