I had the same problem and I fixed it!
In the server folder, click the forge.jar file again. It creates more files and it fixed it for me! Also try deleting the "world" to clear up old errors!
Sorry! I JUST figured it out! Alright, do NOT run the server with the "minecraftserver.jar". Run it ONLY with the "forge.jar".
When you first set up the server, click the forge.jar once to make a mods folder, fill it, then click it again to open the server! I hope this helps!