Maya Rigging and Animation Toolkit

I have been rigging a robot character in Maya 2015 using the epic games Maya Rigging and animation toolkit … I had it all set up hit the build control rig button and created a snapshot … but then when i hit build a error message came up saying :

File contains unknown nodes or data. to preserve this information, the current file type cannot be changed.

File contains unknown nodes or data. to preserve this information, the current file type cannot be changed

Does anyone know what that means / what the problem is and how i can fix it ?

I’m having the same problem. Did you ever figure this out?