During the upgrade of VMware VCenter server to 5.1.1, DO NOT click "Cancel" on the following prompt during the upgrade.
I was upgrading from 5.1.0 to 5.1.1 and during the upgrade i came to the following prompt and by reading the prompt i assume i needed to reboot my server right now in order to continue on which i select "Cancel".
This however caused the upgrade to fail, but not without the upgrade for SSO actually trying to upgrade my environment and corrupting the SSO database and server. Afterwards i could not get Vcenter server to start or any authentication to work.
As with all my work I had a good snapshot and database backup taken before the upgrade.
After a support case with VMware and an hour later or debugging, we could not get SSO working again and we reverted back to the snapshot to start the upgrade process over.
Always take snapshot and databases backup before any upgrade or installation!
This does not just apply for VMware but all applications.