[Konstantinos]

Above this line (at 26):

pawn Код:

new pTrack[MAX_PLAYERS] = {INVALID_PLAYER_ID,...},pTrackTimer[MAX_PLAYERS];

you've forgot a semicolon (; ) at the end.

pawn Код:

CMD:c20(playerid,params[])
{
    switch(pTrack[playerid])
    {
        case INVALID_PLAYER_ID:
        {
            new id;
            if(sscanf(params,"u",id)) return SendClientMessage(playerid,-1,"/c20 [playerid]");
            if(!IsPlayerConnected(id)) return SendClientMessage(playerid,-1,"Invalid playerid");
            pTrack[playerid] = id;
            pTrackTimer[playerid] = SetTimerEx("TrackTimer",1000,1,"i",playerid);
        }
        default:
        {
            pTrack[playerid] = INVALID_PLAYER_ID;
            KillTimer(pTrackTimer[playerid]);
            DisablePlayerCheckpoint(playerid);
        }
    }
    return 1;
}

public TrackTimer(playerid)
{
    new pos[3];
    GetPlayerPos(pTrack[playerid],pos[0],pos[1],pos[2]);
    SetPlayerCheckpoint(playerid,pos[0],pos[1],pos[2],4.0);
    return 1;
}

And for the second one, you missed a : after default.