My root-enumerated audio WDM driver creates a proprietary interface for its control application. Interface is created using IoRegisterDeviceInterface, then enabled using IoSetDeviceInterfaceState. User-mode control application obtains interface path using SetupDiEnumDeviceInterfaces, ensures that SPINT_ACTIVE is set and SPINT_REMOVED is not set, then opens it using CreateFile, then uses DeviceIoControl to communicate with the driver. For thousands of users, all works normally. But I have 5-6 users running Windows XP (SP2 and SP3) who complain to errors. In those systems, CreateFile is completed successfully, returning a valid handle, but the driver does not receive IRP_MJ_CREATE (driver receives no requests from this application at all). Then control application issues DeviceIoControl to that handle but the driver, of course, does not receive IRP_MJ_DEVICE_CONTROL and DeviceIoControl returns ERROR_INVALID_FUNCTION. Here is a log: System: Arch=0 CPU=586 ProcRev=F0B NumProcs=4 ProcMask=F OS version: 5.1.2600 SP 2.0, SPname="Service Pack 2", PID=2, SM=100, PT=1 Finding driver interface... Interface 0: GUID=83ed7f0e-2028-4956-b0b4-39c76fdaef1d, Flg=1 Drv IF: \\?\root#media#0000#{83ed7f0e-2028-4956-b0b4-39c76fdaef1d} Opening \\?\root#media#0000#{83ed7f0e-2028-4956-b0b4-39c76fdaef1d}\0d13c528-a6fc-47f1-8fee-c5dd46f1fbb1 Driver interface opened (DC) IoCtl to DC with 222004, ReqSize=4, ResSize=32 IoCtl returned 0, LastErr=1, RetSize=3435973836 IoCtl failed (0/1 - Incorrect function.) Error: Cannot get driver info (0/1 - Incorrect function.) Closing driver Why this could happen? Regards, Eugene ****************** WDMAUDIODEV addresses: Post message: mailto:wdmaudiodev@xxxxxxxxxxxxx Subscribe: mailto:wdmaudiodev-request@xxxxxxxxxxxxx?subject=subscribe Unsubscribe: mailto:wdmaudiodev-request@xxxxxxxxxxxxx?subject=unsubscribe Moderator: mailto:wdmaudiodev-moderators@xxxxxxxxxxxxx URL to WDMAUDIODEV page: http://www.wdmaudiodev.com/