[Babul]

remove the return 0; after the dcmd's, the rest of the code needs to be executed, even if there ar no more commands. the only important return is the one directly before the end of the callback:

pawn Код:

public OnPlayerCommandText(playerid, cmdtext[])
{
    dcmd(login,5,cmdtext);
    dcmd(register,8,cmdtext);
    if (PLAYERLIST_authed[playerid]==0){
        if (udb_Exists(PlayerName(playerid))){
            SystemMsg(playerid,"You're not logged in yet.");
        }
    }
    return 1;
}

may i suggest you to use another command processor?
edit: maybe i broke your command by removing some returns, but dont hesitate to experiment with them