Why I can not ban the operation of

Question

I write a driver to attach on MountPointManager and filter all IOCTL_MOUNTMGR_DELETE_POINTS IRP. But after I return this IRP with code below, I see no volume letter left.

Irp->IoStatus.Status=STATUS_INVALID_PARAMETER;
Irp->IoStatus.Information=0;
IoCompleteRequest(Irp,IO_NO_INCREMENT);
return STATUS_ACCESS_DENIED;

Anyone could help me? Thanks a lot.