There are a number of posts in the MS forums from users who had significant issues upgrading their Outlook identity for Office 2011.
The upgrade process begins, then you get a message telling you that it failed and you need to repair the identity with a previous version of the Database Utility.
My take on the warning is that the identity had some sort of corruption that the new Database Utility doesn’t know how to fix.
MS posted a Knowledge Base note about the issue with a solution:
Unfortunately, this approach still sometimes fails. There is still an alternate route that has proven more successful:
Either reinstall Office 2011 and update it to at least SP1 (14.1) but NOT SP2 (14.2) or restore Office 14.1.x and use the database utility from this version (/Applications/Microsoft Office 2011/Office/Microsoft Database Utility) to repair your identity.
If it succeeds, you can then relaunch Outlook 14.2 to upgrade, and finally use, your identity for Outlook 14.2.