Speedo stopped working

A4 Avant 2.5TDi automatic...Speedo suddenly stopped working today. Reads zero all the time. Have put the VAGCOM on it - no fault codes. Have run VAGCOM logging during a test drive and it registers correct speed on the laptop.
Removed the instrument cluster and reconnected the plugs. Still no good.
Any ideas?

Well, after testing the speedometer with the VAGCOM output tests, it seems that bit is OK as well.
So disconnected the speedo sensor on the gearbox output shaft (passenger side), sprayed it with a bit of electroclean, reconnected again and now its working.