are you doing this from the RMB, or from windows? Please post screenshots.
IF doing from RMB, I don't believe that c: will copy correctly, it has to be done from within windows, so that c: is unlocked (I have bitlocker also)
to back up a bitlocked partition, you need to do it from within windows. disabling tpm doesn't unlock the bitlocked drive.
try installing in windows, and run from within windows. it will see all your partitions; it will show c: drive, as a bitlocker drive, but UNLOCKED, and will allow the backup