Thank you everyone for your replies.
Howard: The Admin account is definitely a manual account and still logs in successfully on the old 1.9 installation. I have a working copy of the 1.9 production installation running on the same test server as the 2.2 upgrade and it still logs in fine. We are not using external authentication - only manual or LDAP.
You are correct that I cannot log in to perform any troubleshooting. Any solution will either need to occur before I upgrade or in the config/database after installation.
I will try turning on debugging in the config to see if this gives me more information.
Guillermo: I will check these values in the database to make sure nothing has been altered during upgrade. It does seem to be a role issue, I am just at a loss where it might be.
Thank you both for your suggestions.
Reading through the forums, the inability to log in under the manual admin account seems to be a common issue after upgrade. A number of people reporting successful upgrades have still indicated they needed to log in with another account, such as an LDAP account, and that the main admin was broken.
Thanks again for the support.
Frank: I work in an organisation that only uses Windows Server. The previous 1.9 installation has been running successfully and problem free in this environment for 5 years. A copy of the 1.9 production installation is running successfully on the exact same Windows test server as the failed 2.2 installation. This is not an operating system issue. Pursuing this angle would waste my time, I'm afraid. I am also uncertain what poorly managed environments you have worked in where the Windows Servers required reboot every 24 hours. I work in an organisation that runs thousands of Windows Servers - both real and virtual - and such a requirement is not part of standard operations.