This issue was observed due to an incorrect URL specified for the Blackbaud Core Components section. Since the file path was referencing the folder of bbappfx instead of the AppFxWebService.asmx file, this was causing the 405 error to appear. To resolve, perform the following: 
  1. Log into NetCommunity as a supervisor
  2. Click Administration > Sites and Settings
  3. Click the Web Services tab
  4. Locate the Blackbaud Core components section
  5. Update the URL to the following format: http://xxxxxxxxxxx/bbAppFx/AppFxWebService.asmx
    • The xxxxxxx is the domain that should already be in place for that service
  6. Scroll up to the top of the page > Click Save
  7. Refresh the test config page to verify the error resolved