Ok here are the basic steps and make sure you pretty much follow'd them.
1)Make sure you can play NORMAL server games on tremulous.
2)If you can play normal games, proceed to make your map on GTK.
3)Once you have made the map and everything necessary, save and go to the BUILD toolbar on the top edge of GTK.
*If you can't find the menu, I have failed you
4)Depending on which version of GTK you have, the menu will be different. Basically, click on where it says TEST.
5)Wait for the process to end.
6)MAKE SURE THE NAME OF THE NEWLY CREATED BSP DOES NOT SAY "map.bsp.bsp" or anything like that.
7)Start Trem and at the main menu hit the squigly "~" key and type "/sv_pure 0"
8)If you have done all that is in your power to follow these instructions and it STILL doesn't work, go to the troubleshooting section as your client is probably bad.