I'm making a thread so I don't forget how I successfully reinstalled my DT50 Head flash memory. It may help someone else out there in Line 6 land.
Here's my instructions: DT50 Head Flash Memory Update; First update MIDI Device (MIDISPORT Uno) Go the website and download and install the most recent driver. Connect the MIDI cable properly and turn on Amp, I leave it instandby with speaker connected. Open the Latest Version of Line 6 Monkey, Click the "Change Device" button, Cilck the "I don't see my device" Button, in the next window select "Connect Using MIDI Cables".
In the next window (MIDI Connection Configuration) select MIDI Out and select "MIDI Uno Out" and "MIDI Uno In" then select your specific "Line 6 Device" and when you click "ok" all those windows will close. Now you can initiate the Flash Memory Update.
Basicly your setting the MIDI Parameters before the update. I have to do this everytime I want to reflash if I don't I'll get the "incorrect parameters" (Code x80000002) error message.