How to fix "Theme cannot be found errors"

Wiith the following Website structure.
- Default Web Site
  - vdir1
    - App_Code
  - App_Code
  - App_Themes
    - GlobalTheme

when I queried for a page http://localhost/vdir1/Test.aspx, I got the following error message "ConfigurationErrorsException: Theme 'GlobalTheme' cannot be found in the application or global theme directories". The fix for this was simple. I had to create a sub-folder named App_Themes under vdir1 as shown below.

- Default Web Site
  - vdir1
    - App_Code
    - App_Themes
      - GlobalTheme
  - App_Code
  - App_Themes
    - GlobalTheme