“Outlook Web App couldn’t initialize A base theme couldn't be found. The base theme must be in a folder with name = "base" after installing Exchange 2010 SP1 rollup 6

I ran into a problem with one of our customers , he was installing Exchange 2010 SP1 rollup 6 and while testing functionality post rollup installation he figured that OWA is not working [ Blank page is given with URL similar below :

https://mail.itguydiaries.net/owa/auth/logon.aspx?url=https://mail.itguydiaries.net/owa/&reason=0

Upon investigation , I found the following set of errors / warnings at server’s application log :

This is a common issue with Exchange Server rollup installation results from failure of rollup to execute UpdateCAS.ps1 script as a part of rollup installation process .

In order to solve this issue all is required is to execute UpdateCas.ps1 located at C:\Program Files\Microsoft\Exchange Server\V14\Bin .

Once the script is executed , followed by restarting IIS [ iisreset from EMS ] , the following event appeared at application log indicating that Outlook Web App is ready.

Finally , testing with a browser showed that OWA works just as it should