Ptex paint layer won't export
 

This is not strictly just a maya issue, but I'm hoping texture artists will be familiar with using mudbox to Ptex paint textures for maya.

Using mudbox2015, I have a model with a painted texture, set up for ptex.
I have one paint layer, I select it and I rmb click>export selected. It processes it and the progress bar shows 100% (extracting...). But when it once it finishes, it fails.

The error window is as follows:



I click ok, then the following window says:



reaper8_texture_polySurface4 is the paint layer name.

Reaper_Painted is what I named the file in the save as window.

As I look at it, the file path looks weird, with two filepaths in it, and the filename says .ptx.ptx. So a double filetype. I thought maybe that was the problem but I'm not sure. I've tried to change the file name of the mudbox file, tried omitting .ptx in the save as... filename box, even changed the windows setting that hides file extensions. Nothing has worked.

What I'm trying to do, is extract the paint layer to assign to an identical model in maya as a texture.

Please help me make this work!