If you get this message on your TYPO3 instance, the lockingMode configuration settings is set to disable.
You can configure it in the TYPO3 install tool in the backend, and it is saved in typo3conf/LocalConfiguration.php in TYPO3 6.2:
$TYPO3_CONF_VARS['SYS']['lockingMode'] = 'disable';
The install tool writes about lockingMode:
[SYS][lockingMode] = disable
String: Define which locking mode is used to control requests to pages being generated. Can be one of either disable (no locking), simple (checks for file existance), flock (using PHPs flock() function), semaphore (using PHPs sem_acquire() function).
Default is simple.
The default value on our installation was disable :/