Try this:
*Go to your MTA folder, then server and open "MTA Server.exe".
*If you haven't errors, open Multi Theft Auto, go to QUICK CONNECT and click in Local. Then connect to the server (is your own server).
*Write in the server's console (MTA server.exe) "start editor", without the quotes. Can you make maps now?
If you have errors, try to re-install the latest version of Multi Theft Auto, click HERE.
It works? If not, please install and run MTADiag and follow the instructions.