Windows 2k3 Server: iSCSI Session cann't Logout when using MPIO DSM

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We have developed DSM driver based on Microsoft MPIO framework. However, when I login my storage by iSCSI（Initiator 2.08 on W2K3 SP2 x86）, I can't logout the iSCSI Initiator session on the "Targets" tab and then "Details" button as I get the following error："The session cannot be logged out since a device on that session is currently being used." the explaination of the problem is that there is a device being used . In fact we donot use any device. If so how to explain the session?

we have tested some other samples ( like msdsm, gendsm) provided by Microsoft and the same errors occured again.

How do I deal with this situation? Thank you so much.