ERROR on PO Auto Number Generation

ERROR #2147217913 

Conversation failed when converting the nvarchar value '********' to data type int.

(Source: Microsoft OLE DB Provider for SQL Server)

(SQL State: 22018)

(NativeError: 245)

No Help file available

SET NOCOUNT on
select ISNULL(max(cast(right(ponumber,7) as int)),0) + 1 asnextponumber from PurchaseOrder where ISNUMERIC(ponumber)<> 0

I know

Hotfix #32

KB2735491

Suppose to Fix it but i get an error message 

The expected product version is not installed

Is there a way in SQL to fix this like Alter the command

the VARCHAR works 

select ISNULL(max(cast(right(ponumber,7) as varchar)),0) + 1 asnextponumber from PurchaseOrder where ISNUMERIC(ponumber)<> 0

Would this command change or alter function if entered as

SET NOCOUNT on
select ISNULL(max(cast(right(ponumber,7) as varchar)),0) + 1 asnextponumber from PurchaseOrder where ISNUMERIC(ponumber)<> 0