[Nero_3D]

The ALS hook must be after the function!, also use hook method 7
The reason is simple because you redefine the function name

PHP код:

public OnPlayerEnterDynamicRaceCP(playerid, checkpointid)
{
    #if defined dym_OnPlayerEnterRaceCP
        return dym_OnPlayerEnterRaceCP(playerid, checkpointid);
    #else
        return true;
    #endif
}
#if defined _ALS_OnPlayerEnterDynamicRaceCP
    #undef OnPlayerEnterDynamicRaceCP
#else
    #define _ALS_OnPlayerEnterDynamicRaceCP
#endif
#define OnPlayerEnterDynamicRaceCP dym_OnPlayerEnterRaceCP
#if defined dym_OnPlayerEnterRaceCP
    forward dym_OnPlayerEnterRaceCP(playerid, checkpointid);
#endif
// in another file
public OnPlayerEnterDynamicRaceCP(playerid, checkpointid)
{
    return true;
}