What does ClearCommError rc=24 mean?

I'm using OverlappedIO and I'm calling ClearCommError inbetween reads.  But I've noticed that I get ERROR_BAD_LENGTH (24) for most of my calls (cbInQue and cbOutQue are both zero as well).   In the examples, most people are checking for ERROR_IO_PENDING -- I get that.   But the MSDN help for ClearCommError doesn't even list ERROR_IO_PENDING as a value for dwErrors let alone ERROR_BAD_LENGTH.   So where do I find what this error code is trying to tell me?

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rhfritz