Unable to export displacement map in MudBox

TheAxiom

I'm getting an error "Mudbox cannot use the "Subdivision" Locate Method on these meshes, because they do not have the same base-level topology. Set Locate Method to "Raycasting" and try again."

http://prntscr.com/69q47a

I've tried setting it to raycasting and I get the same error.

I've got a plane in the centre of my terrain geometry like this
http://prntscr.com/69q4j3

I've done it successfully in the past, but I did get an error importing the terrain mesh in to Mudbox saying that the subdivision levels needed to be rebuilt, but when I click "Rebuild Subdivision Levels" nothing happens.
http://prntscr.com/69q713

My baking settings
http://prntscr.com/69q57d

TheAxiom

Okay I exported and re-imported the terrain a few more times and it finally let me rebuild the subdivision levels. That fixed it.
It was just MudBox being a butt.

Another quick question while I'm here, how do I get rid of the borders that MudBox makes with height maps? It's like bleed or something.