This is how I create GMAPs and I've never had any issues-
- Create the GMAP file (ensure the WIDTH and HEIGHT are correct)
- Load the Levels & GMAP in to the relevant FTP folders (i.e. levels/gmaps)
- Add the GMAP file name to the 'GMAPS=' in server options
- Add 'loadmap GMAPNAME.gmap' to a weapon which is added to the player on login
- Finally warp to the GMAP and it will work
I've created many in the past not in this order and they've always had issues. :[