If you've changed the name of the gamemode:
Look for this in server.cs
if($GameModeArg $= "Add-Ons/GameMode_SpeedKart/gamemode.txt")
activatePackage(GameModeSpeedKartPackage);
And change GameMode_SpeedKart to the name you gave to the gamemode.
Also, if you haven't already, you need to change it in the gamemode.txt too. Find:
//Kart racing stuff...
ADDON Brick_ModTer_BasicPack
ADDON Brick_ModTer_InvertedPack
ADDON Brick_Modter_4xPack
ADDON Print_ModTer_Default
ADDON GameMode_SpeedKart
ADDON Server_VehicleGore
ADDON Event_Camera_Control
Again, change GameMode_SpeedKart to the name you gave to the gamemode.