Reading Third party Maps

Correct, I hold most of my 3rd party maps on a usb stick permanently connected to a rear port on my PC. It may not even need an unlock code, that code (if one is required) is really only needed for maps installed to devices.

Thanks. That solves the problem of browsing the map on the MAC with Basecamp. Now if I want to keep the map in the device memory and not on the SD card, how should I move it? I see that 2455 has a Map folder and also a .System folder. The primary mapset is in the .System folder. And I presume the supplementary map should go to the Map folder. But where should I keep the unlock file? I tried with Map folder, System folder as well as the main Garmin folder. Every time I get a "cannot unlock map" notification on the device.

The unlock file for any map must be in the same folder as the map. Assuming by the primary mapset you mean the CN map then it should have a .unl and .gma file associated with it. What is your supplementary map?

Since I am based out of India, I deleted the CN map (as I dont need it) and moved one of the free unlocked map as gmapprom.img (Dont need a unl for it). But I do see a .gma but its not associated with this base mapset. The supplementary map that I have is mapmyindia maps for India. I dont see the "cannot unlock" error when I dont copy the supplementary map into Map folder. Only when I do that I see the "cannot unlock" error.

Please note: I am just copying the supplementary map into the internal memory and not installing it via Basecamp/Mapsource. If there is a difference between the installation by Basecamp vs just copying IMG/UNL file, please do let me know.

OK, well the .gma is possibly remaining from the CN map, if so it will be named gmapprom.gma and have the same date the map did. You can delete it.

Now why you're getting a 'can't unlock maps' message I don't know IF the maps you've loaded are unlocked. It could simply be your nuvi seeing a .gma file and wanting a corresponding .unl file, so first see if deleting the .gma fle helps.

If you're still getting the message try a master reset.

If you're still getting the message try a master reset.

I deleted the .gma file (it was not gmapprom.gma). Now the error changed to "cannot authenticate". Trying to debug now.

Then that file is associated with a map on your nuvi. You get a 'cannot authenticate map' when a .gma file is missing and a 'cannot unlock maps' when a .unl file is missing.

Your problem (assuming you're correct about the 'free unlocked map') must be with the mapmyIndia map, I suggest you reinstall it.

Thats the whole question which I am now trying to resolve. How do I re-instal the mapmyindia map on the device internal memory. It works with SD card. But not on the internal memory.

If it works on the card just copy the map files into the Map folder on your nuvi.

That did not work too. I tried the traditional method : (Windows) gmaptool -> split -> cgpsmapper -> mapsettoolkit -> MAC export -> Basecamp. But I am not able to install it in mapsource iteself. Thats another parallel thread that I am not able to unravel. The same approach works in other cases. I have many other maps installed this way in my MAC. But this one eludes me. Trying to debug the problem in parallel in windows.