On certain models...like the 2010+ 170CR diesel the ECU is locked, it cannot be flashed via the OBD port. So, you have to remove the ECU, use the REVO SPX unit to probe the ECU to remove the lock, and then either flash it on the bench or reinstall the ECU and use the OBD port like normal.
Absolute ball ache for Alex, something that should take 20-30mins max. ends up taking about 2-3 hours.