I have had this symptom several times over the years on my saloon car(s) - the solution has always been to put the vehicle in gear and to rock it back and forwards - the teeth of the drive dog on the starter (bendix gear) have failed to engage with the flywheel and have just jammed up against it - rocking the vehicle in gear just moves the flywheel enough for the bendix gear to retract.
I have no experience with large vehicles - I just guess...
Good Luck...
January 2017