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OWA broken with error “A base theme couldn’t be found”


When trying to access OWA it does not load, and eventually will show an error stating a base theme couldn’t found.


All of the OWA themes are located in the following directory C:\Program Files\Microsoft\Exchange Server\V14\ClientAccess\Owa

You will notice different folders with different version numbers. In this case the version number was 14.1.438.0. It was created by a recent update. OWA uses the most recent version. If you open the folder, then themes, and then base, you will notice the folder is empty.

  1. Open Exchange Management  Shell as admin
  2. Run the following command – cd ‘C:\Program Files\Microsoft\Exchange Server\V14\Bin’
  3. Run the following script – UpdateCas.ps1
  4. It will copy the correct files into the base directory and register them, OWA should now work
  5. Before testing it I ran “iisreset” from an elevated cmd prompt, but I am not sure if that made any difference