Semaphore Warning: semop() failed in release_sysvsem_sem for key

Denne kode skulle gerne bevirke at kun 1 tråd/bruger kommer igennem af gangen.
Denne fejl kommer desværre bare op hvis 2 kører den samtidigt.
"Warning: semop() failed in release_sysvsem_sem for key 0x1: Invalid argument in Unknown on line 0"
Er der nogen der ved om jeg har lavet en fejl, eller hvad der ellers måtte være galt.

//instantiate shared memory and semaphore
$MEMSIZE    =  2048;//  size of shared memory to allocate
$SEMKEY    =  1;  //  Semaphore key
$SHMKEY    =  2;  //  Shared memory key
//instantiate finished

  $sem_id = sem_get($SEMKEY, 1); // get the information about semaphore, if this does not happen, page reloads
  if ($sem_id === false)
  {
    ?><script language="JavaScript">
    window.location.reload(true)
    </script><?
  }
  else
      //echo "Got semaphore $sem_id.\n";

  // Accuire semaphore
  if (! sem_acquire($sem_id)) // try to get the semaphore, if the semaphore is allready taken, page reloads
  {
      sem_remove($sem_id);
    sleep(3);
    ?><script language="JavaScript">
    window.location.reload(true)
    </script><?
  }
  else
    $shm_id =  shm_attach($SHMKEY, $MEMSIZE); // get information about shared memory access, if problem, page reloads
      if ($shm_id === false)
      {
          sem_remove($sem_id);
        sleep(3);
        ?><script language="JavaScript">
        window.location.reload(true)
        </script><?
      }
      else
    $var1 = 0;
    $var1  =  shm_get_var ($shm_id, 1); // read information about shared memory
    echo ("Tidspunktet for sidste kørsel: ". $var1."<br>");
    $timestamp = time();
    $date_time_array = getdate($timestamp);
    $timestamp = mktime($date_time_array['seconds'], $date_time_array['minutes']);
    $seconds = $date_time_array['seconds'];
    $minutes = $date_time_array['minutes'];
    if ($minutes < 10) //if there is less then 10 minutes in the hour put a zero in front
    $minutes = "0".$minutes;
    if ($seconds < 10) //if there is less then 10 seconds in the minute put a zero in front
    $utime = $minutes."0".$seconds;
    else
    $utime = $minutes.$seconds;
       
    if ($utime <= 4) //If the time has changed to a new hour and the utime is with in 4 seconds of this, page reloads.
    {
            sem_remove($sem_id);
        sleep(2);
        ?><script language="JavaScript">
        window.location.reload(true)
        </script><?
        exit;
    }
    $seconds_old = $var1{2}.$var1{3};
    if ($seconds < 4 && $seconds_old > 56) //if there is a change in the minute 40 seconds is applied
    $var1 = $var1 + 40;
    if($var1)
    {
        $test = $unlocktime-$var1;
        if ($test <= 4 && $test >=0) //If there is less then 4 seconds between the utime and var1(shm utime), page reloads
        {
                sem_remove($sem_id);
            sleep(2);
            ?><script language="JavaScript">
            window.location.reload(true)
            </script><?
            exit;
        }
    }
  // Write variable 1
  if (!shm_put_var($shm_id, 1, "$unlocktime")) //try to write utime to shared memory. If not possible, page reloads
  {
        sem_remove($sem_id);
    sleep(2);
    ?><script language="JavaScript">
    window.location.reload(true)
    </script><?
    exit;   
  }
  // Release semaphore
  if (!sem_release($sem_id)) //try to release semaphore. if not possible, page reloads THIS IS BAD!!!
  {
        sem_remove($sem_id);
    sleep(2);
    ?><script language="JavaScript">
    window.location.reload(true)
    </script><?
    exit;   
  }