According to Graeme Fowler, downgrading the system software on the GPS V to the previous version 2.40 corrects the issues with detecting and using the European EGNOS satellites to obtain a differential lock.
However, the drawback is – as with any downgrade of firmware on the GPS V – that you will lose all your previously stored waypoints, routes and indeed any other user data, so be sure to use Mapsource to backup all of that information before you proceed with this.