You can use these two snippets, I got them from a bog I believe:
--SQL 2005
UPDATE msdb.dbo.sysdtspackages90
SET ownersid = 0x01
where packagetype = 6
--SQL 2008
UPDATE msdb.dbo.sysssispackages
SET [ownersid] = SUSER_SID('sa')
where packagetype = 6
Andrew