shmop_open(): unable to attach or create shared memory segment 'No error'

[bohzio]

If I only save and get one line it works:
$memory = new Block;
$memory->save('key1', 'value1');
$memory->get('key1');

But if I run your example:
$memory = new Block;
$memory->save('key1', 'value1');
$memory->save('key2', 'value2');
$memory->get('key1');
$memory->get('key2');

There is an error on the second save.
The error start on $id = shmop_open($this->id, "n", $this->mode, strlen($data));
Do you know what is the problem?
Thank you