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