Error Invalid Column Name (In Sqlserver 2005) While Giving Alias Column Name

ALTER procedure [dbo].[MyPro](@StartRowIndex int,@MaximumRows int)

As

Begin

Declare @Sel Nvarchar(2000)set @Sel=N'Select *,Row_number() over(order by myId) as ROWNUM from MyFirstTable Where ROWNUM

Between ' + convert(nvarchar(15),@StartRowIndex) + ' and ('+ convert(nvarchar(15),@StartRowIndex) + '+' + convert(nvarchar(15),@MaximumRows) + ')-1'

print @Sel

Exec Sp_executesql @Sel

End

 

--Execute Mypro 1,4        --->>Here I Executed

 Error

Select *,Row_number() over(order by myId) as ROWNUM from MyFirstTable Where ROWNUM

Between 1 and (1+4)-1

Msg 207, Level 16, State 1, Line 1

Invalid column name 'ROWNUM'.

Msg 207, Level 16, State 1, Line 1

Invalid column name 'ROWNUM

Procedure successfully created but giving error while Excuting'.

Please anybody give reply

Thanks