HttpAddUrl returns with error ERR_INVALID_NETNAME

Question

I'm creating a HTTP server by doing the following:

retCode = HttpInitialize( 
            HttpApiVersion,
            HTTP_INITIALIZE_SERVER,    // Flags
            NULL                       // Reserved
            );

retCode = HttpCreateHttpHandle(
            &hReqQueue,        // Req Queue
            0                  // Reserved
            );

retCode = HttpAddUrl(
            hReqQueue,          // Req Queue
            localUrl.c_str(),   // Fully qualified URL
            NULL                // Reserved
            );

localUrl would be something like http://192.168.1.x/someUrl or http://37.123.43.x/someUrl. The base URL obviously doesn't change in between adding Urls.

HttpInitialize and HttpCreateHttpHandle return success. However, HttpAddUrl returns with error 1214 (ie. ERR_INVALID_NETNAME) when I use a non-local IP address. I'm starting the program as an administrator.

What can the problem be?