After an initial email enquiry and a telephone discussion, an initial analysis of the problem was provided, which later proved to be spot on.
Vehicle is a BMW 730 on an 06 plate - GPS initial start-up showing "Initializing" message, hanging for a minute or so, and then an error message saying "Cannot read disc, place disc in CD/DVD Drive.
BMW quoted £2700+ to rectify the problem and Revtronic did the job with new (exchange) equipment and labour cost for a tad over £200.
Their fault diagnosis was spot on, their customer service was spot on and overall, I highly recommend these guys to anyone who has problems with their in vehicle GPS system.
Work was completed in about 30 minutes, I tested the system for around 20 minutes or so, and left their premises a very happy person.
Two days on and the system is working perfectly and just as it should.