its because of the uv protection on the windscreen matey, it blocks the gps transmission
if you look in the centre of the sreen at the bottom there is a little window which hasnt got the uv, if you place the road angel in this bit you will get reception, this bit is kept clear so the french toll road scanners can swipe the barcodes for the toll passes
alternativley you can get an external antenna from ebay or online stores for a tenner and plug it into the road angel, you can then stick the antanna either outside on the scuttle panel at the front or run it under the trim to the rear screen (mines in the rear screen)
andy