It happens, for no reason you flash a perfectly good tune in a car and the car does not start or cuts out and OBD recovery is not available.
You’ve Bricked the ECU.
Usually this happens when the ECU is already tuned by third parties or you’ve flashed with the wrong file/bad file.
To unlock follow this procedure (valid for CMD Flash):
1) Open up the ECU (or use bench boot if available).
2) Read the ECU password with Fxx (not needed for bench boot).
3) Read the ECU backup with tricore boot or bench boot.
4) Open the backup in the tricore backup manager.
5) Export the flash with calibration area. Usually IROM2.
6) Modify one value and do not calculate the checksum.
7) Import the modified file back in the backup.
8) WRITE the modified backup via tricore boot or bench boot.
9) The ECU now has a bad checksum in the calibration area and allows for OBD flashing again. You can tell as the engine cooling fans run on high speed.
10) Now write the original file read by obd into the ecu via OBD.