This article provides some suggested troubleshooting steps. 

I am getting a server error response when trying to reach the Web app address.

Error message

404 - File or directory not found. 

Resolution

Check the following: 

1. Launch the IIS Manager.
2. Navigate to the app site.
3. Double-click on Request Filtering in the main pane.
4. Click on Edit Request Filtering Settings. The settings should look as follows:

A restart of the IIS service is recommended after the changes have been applied.