Use CallClientFunc
Something like this:
Server-side:
function onPlayerJoin(p)
{
if (Reg[p.ID] == true) CallClientFunc(p,"testscript/testscript.nut","IsRegister",true); //send to client infomation about register status
}
Client-side
Register <- false;
function IsRegister(bool) Register = bool;
function onClientRequestSpawn(c)
{
if (Register == true) return 1; //can spawn
else return 0; //can't spawn
}