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You have to connect the higher level mesh and the lower level mesh with an off mesh connection, it's under the mesh editor, you can also read the tutorial for it in the wiki or the guides section. If your character is repeatedly getting stuck in the same position you most likely have meshed an area your character can't actually access, so you have to delete that part of the mesh that your character cannot walk on. You can do this by holding Alt and Right Clicking the parts of the mesh that are causing the problems.

You can also lower your radius for meshing and force mesh each individual triangle there as well in areas that happen to be narrow.