DUA Cannot Connect to the Web Server

When the DUA service runs, it cannot connect to the Web server.

The following list provides several areas of configuration that can help identify problems.

Use the Event Viewer for the DUA service to see the relevant WinHTTP error code. From a command line, type eventvwr.

Use the error code that is listed in the event viewer to troubleshoot your connection to the Web server. If DUA is unable to connect to the server, the error code will be a WinHTTP error code. More information about WinHTTP error codes can be found at this Microsoft Web site.
Review your Web server's access logs to determine the error type that was returned to the client. Typically, 404 errors denote a problem accessing the file, 403 errors denote client authorization errors.
On the device, verify the port number that is used to access the Web server. By default, port 80 is used for HTTP access and 443 is used for HTTPS access. On the server, verify that the Web server is configured to use these ports.
If you are using HTTPS, verify that both the client and server are configured to use the appropriate authentication types. Use either a user account (specified in the DUA registry settings), or a certificate authentication type. If you are using IIS, use a Certified Trust List (CTL) and use client certificate mappings. For more information, see your IIS documentation.

Additional resources