Upgrading from 5.5 SSO to 6.0 PSC is usually pretty easy but I did have one error worth mentioning.
First I got the generic 1603 Error.
I then looked through the logs and saw this:
“Unable to call to Component Manager: Failed to register service in Component Manager; url:http://localhost:18090/cm/sdk/?hostid=5e7af582-c545-11e5-a7c6-005056b8654e, id:04d333a2-e2bb-41c8-8ae6-39598604ddc1”
After working through it with support, it turned out I was missing a PTR record. Once I created that my upgrade was successful.
NOTE: As with any of the 5.5 to 6 upgrades, a failure will trash your system. Restore from your snapshot and upgrade again.