Users receive a blank page when they try to log in to Outlook Web Access (OWA).
This problem may appear after the Exchange 2010 SP1 Rollup 5 installation on the servers with CAS role.
To fix this problem you must start the updatecas.ps1 script in the Exchange Management Shell. You can find the script in the C:\Program Files\Microsoft\Exchange Server\V14\Bin directory. This script comes with the update rollup.