I've just overcome this issue on my laptop with Win10.
What I was doing:
1. installed the newest M-Audio drivers
2. connected M-Audio Uno into laptop's USB2.0 port. My laptop also has USB3.0 interfaces but Uno doesn't work with them
3. connected M-Audio Uno into DT25 Head
4. switched DT25's Power on
5. opened Monkey, chose amp and in/out MIDI ports
6. logined into my account in Monkey. I've registered amp in my account few days before I updated it
7. reconnected my DT25 in Monkey
8. downloaded flash file from Line6 site
9. started update by file (not by server)
After these steps my DT25 updated.
