Hello,
Did you try playing back the RTMP stream using the following URL format?
rtmp://myIP:80/myApp/ngrp:MyStream_all
The URL format you are trying is specific for Adobe HTTP stream, but you are using the rtmp://. It should be http://, like this:
http://myIP:80/myApp/ngrp:MyStream_all/manifest.f4m
Zoran