If you have a supported RTMP server, first make sure it's running and accessible.
Also, make sure you install rtmp side as explained on:
http://www.videowhisper.com/?p=RTMP+Applications
And fill rtmp address as explained there rtmp://ip-or-domain/videowhisper .
Default rtmp port is 1935 so don't use :5080 for rtmp as that will lead to red5 http not to red5 rtmp.
Call.failed means it can't find rtmp side videowhisper functions to call. Install as mentioned above and restart red5.
As forums are not monitored, for assistance you can contact support team from http://www.videowhisper.com/tickets_submit.php