Basically this thread: http://forum.paradoxplaza.com/forum/showthread.php?691795-Issues-with-custom-maps-1.10
All custom maps that worked fine with 1.09 stopped working with 1.10; The addition of traversable rivers added the possibility to edit in portages and major_rivers in the adjacencies file. The problem is that you NEED a portage for your map to work. If you have a map that doesn't contain a portage the game won't properly load. This is the reason why there are plenty mods that struggle(d) to update to 1.10. You basically have to draw in a piece of navigable river and a lake or two separete major rivers to make it work.
In my opinion this isn't necessary: The engine should be able to work fine even without any of this (but of course I don't know your code).
We talked about it last time we played, said I was going to look into it when I get time