Map change

Hey so I have this problem that when I try to change the map on my Server it always chooses the default map therefore no map change can be done.

If the map is gm_flatgrass (default map) and I try to change it to gm_map2, the map will still be gm_flatgrass after gmods "map change".

Now my question is, is it a Server Issue or a Issue of my Hoster? (Gportal)