Could not install OS to drive C using SCCM 2012 OSD Task Sequence and USMT to Migrate User Profiles

I am using OSD task sequence to install Operating System image to a new PC. I am using USMT to migrate user profiles. Everything works fine except that the OS is always installed to Drive D. I want it to be installed on drive C. I have used task sequence variable OSDPreserveDriveLetter with a value of False before Apply OS in task sequence. It does not work. I have tried using both captured image and DVD image. No success. Help Needed.