2002 VW Passat brake problem

My brake pedal would not depress while driving my 2002 VW Passat wagon 2.8L V6 ABS, 51K miles on engine. Occurred in no traffic & at low speed, thank goodness. NO warning lights came on (never have). Car was purchased new from VW dealer & same dealer has done all maintenace. Dealer mechanic kept car for five days & could not find cause nor get brakes to replicate problem. (i) has anyone encountered same problem? (ii) ideas for cause? (iii) how is 2007 Passat wagon?