When using the charging cable provided with my Garmin Nuvi 2597 I can only charge using the USB on my pc which takes an absolute age and is inconvenient because I often need to use both the USB outlets on my PC at the same time for other things. When I use an Apple plus with a USB outlet a message pops up to say that "this cable will not charge your Garmin, please use a Garmin cable" BUT I am using a Garmin cable!!! What is the problem and what can I do about it? Please simple language because Im not much of a techy.