Problem with sem_get and semaphores

Hi, I am trying to do a sem_get on a semaphore that has already been created by a c program. Instead of getting back the semaphore id, I get: Warning: semget() failed for key 0x576a: Invalid argument in /usr/local/apache/htdocs/bioace/testshmop.php on line 5 I can see the semaphores by using "ipcs" and they appear to be there with good permissions, etc. If I call sem_get with a new id everything seems to work fine - the problem is only if I try to interact with a semaphore created by another program. Can sem_get not talk to semaphores in the outside world? Any help is greatly appreciated. Thanks, Rick