Troubleshooting: "An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed" error

This means an error has occurred but due to configuration (perhaps in the machine.config) the error cannot be displayed. Firstly, ensure that the user is running it on the machine that has the API installed.

If it is running on the machine with the API installed, to show the error, change the API's web.config file to add this tag to the inside of the system.web element:

<customErrors mode="RemoteOnly"/>