…I would suggest rebuilding your Outlook identity.
Launch Outlook pressing the option key down to get to the database utility.
Rebuilding the identity will:
- Ensure you are upgrading a somewhat clean identity
- Automatically create a backup of your current identity in ~/Documents/Microsoft User Data/Office 2011 Identities in case something goes bad during the upgrade (there has been numerous reports of corrupted identities that failed to upgrade).
In case you didn’t use these steps and your identity failed to upgrade, MS now has a Knowledge Base article providing instructions on how to get out of this mess: