Try removing the 128MB card completely and just put in your larger card into the internal slot (leave the 128mb one out for now). Then you should be able to run Map and download maps.

The way I see it, the first time you run Map it installs its config area onto the internal card. Then even if you swap the cards around, if it finds a card with its Map config on it, it will continue to use that one.

Thats why you need to remove the 128MB card completely, install the big card into the internal slot and run map again. I had the exact same problem and this fixed it.

Afterwards you might be able to remove all the map config from the 128MB card and swap the cards back around, I haven't tested that.