This is the nearest in client_process.cpp  i come to the line posted.. 
 if(GetLevel() >= spells[memspell->spell_id].classes[GetClass()])
		QueuePacket(app);
	else{
		Message(13, "Unexpected error: Class cant use this spell at your level!");
		return;
	}
Is it the right one ?  can't seem to find it elsewhere...  Noob that I am in this prg 
