InnoDB: Assertion failure in thread ... in file sync0rw.ic line 495 (2 replies)

Hi,
I'm getting the assertion failure, can someone tell me what this assertion is all about ?
I'm not sure if I can ignore the assertion.
Thanks,
Hiromichi

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offending line is
ut_ad((lock->lock_word % X_LOCK_DECR) != 0);
in void rw_lock_s_unlock_func()

111206 12:33:49 InnoDB: Assertion failure in thread 3076225904 in file sync0rw.ic line 495
InnoDB: Failing assertion: (lock->lock_word % 0x00100000) != 0
InnoDB: We intentionally generate a memory trap.