Caloma55

I understand that the Alhambra has the same gearbox and basic running gear as the Galaxy. When I select reverse, nothing happens. The selector lever moves into reverse but the gear does not engage. The car drives fine when going forward. Diagnostic performed by VW main dealer does not show any fault. My garage does not know what to do. The car is 5 years old with 100K miles on the clock. Has anyone any ideas? Any help/suggestions greatly appreciated.