File system filter driver unloaded!

Hi,
I would like to know the consequence of unloading file system filter
driver after I make sure that the IRP count becomes zero as found in filemon
source code.
All the time I can successfully unloaded the driver in my machine. While
in another machine, sometimes it crashed during driver unloading with the
Bug Check 0xCE:

DRIVER_UNLOADED_WITHOUT_CANCELLING_PENDING_OPERATIONS

How to solve this intermittent problem? Any information is appreciated!

Thanks.

-Sin Lam