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