When you upgraded to SQL 2008 from SQL 2005/2000 make sure to change tempdb database Page_verify_option set to CHECKSUM.
By default in SQL server 2008 Page_verify_option is set CHECKSUM but in SQL 2005 the default is NONE.
You can run the below query to check:
select name,Page_verify_option from sys.databases where name='tempdb'
0 - NONE
1 - TORN_PAGE_DETECTION
2 - CHECKSUM