Unable to access Outlook Web Access (OWA) after installing Update Rollup 1, 2, 3 or 4 – flogon.js errors
If you’re having trouble accessing OWA after updating Exchange 2010 with any of the Rollup packages, try this:
Uninstall the update package from the Programs and Features control panel
Download the package file directly from Microsoft, don’t use Windows Update
Open a command prompt or PowerShell prompt as Administrator
Navigate to the location of the package (.msp) and run from the elevated command prompt.
Apparently when Windows update installs the package it doesn’t run it with the elevated privileges to write to the folder in the Exchange program files – why, I have no idea!