If you are getting the following message (on Linux):
Warning: msg_get_queue() [function.msg-get-queue]: failed for key 0x12345678: No space left on device in /path/to/script.php on line 1
aside from what [others have] suggested, you should also check and set an appropriate value for kernel parameter kernel.msgmni, e.g. sysctl -w kernel.msgmni=256