It took me 4 hours to re-import some tables from an Oracle database using SSIS. It kept coming up with Primary Key Violations at random points during the import.
I finally found this http://support.microsoft.com/?id=972498, and after rebooting the server everything worked fine. It seems that the server was running low on memory - even though it's got 16GB of memory. I suspect that it might have been because it hadn't been rebooted in 6-8 weeks.