(Urgent) Help Needed With This Query.

Hi,
I am using this stored procedure to populate a report... if the particular report value is NULL i am getting this error

Cannot read the next data row for the data sest PlanEligiReqattri. Invalid lenght parameter passed to the right function...

This is my stored procedure



Code Block
ALTER Procedure [dbo].[rpt_PlanEligiReqAttriApplied]
@PlanId int
AS
BEGIN
Declare @List varchar(255)
Set @List =' '
Select @List = @List + ', ' + PERA.Name

From PlanEligibilityReqAttriApplied PERAA
Inner Join PlanEligibilityReqAttributes PERA on PERAA.PlanEligibilityReqId = PERA.PlanEligibilityReqId
Where PlanId = @PlanId
select Right(@List, Len(@List) - 2)
--set @List = Right(@List, Len(@List) - 1)
End








any help will be appreciated.
Regards
Karen