Becker Cascade Nav not working - any ideas?

[Roofas]

Just had a Becker Cascade 7944 fitted a couple of days ago and after I spent 3-4 hours figuring it out everything is working fine except the Navi - the positioning isn't updating and just seems stuck with my GPS position about 1/4 mile away.

The fitters are shut for the weekend so I thought I'd post here for any help