I'm speculating, since I don't have your problem; my (clean install of) Win 10 Developer Preview (now upgraded to RTM?) works with TC without issues.
I wonder if there's a problem with the IDs for mounted devices (possible duplication?) as a result of the upgrade (from what OS?). Look in the registry at HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices, where the mapping between IDs and drive letters (as created in
diskmgmt.msc) is stored.
You can flush the entries by removing/unmounting all but fixed drives, and running
mountvol /r from an admin command prompt. (You'll need afterwards to recreate the drive letters you want to pre-allocate to eg removable drives in