apache error - BBS

請教一下
apache error log 出現大量像這樣的訊息

critical_acquire() failed: No space left on device
critical_release() failed: No space left on device
critical_acquire() failed: No space left on device
critical_release() failed: No space left on device

是什麼原因造成的呢?
硬碟空間確定足夠

top:

Mem: 217M Active, 158M Inact, 81M Wired, 18M Cache, 60M Buf, 25M Free
Swap: 2048M Total, 236K Used, 2048M Free

FreeBsd 4.11 Apache/1.3.34

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