[MtoA] The renderer ‘arnold’ used by this scene, is not currently available

// Warning: file: C:/Program Files/Autodesk/Maya2017/scripts/others/supportRenderers.mel line 64: The renderer "arnold" used by this scene, is not currently available. The "mayaSoftware" renderer will be used instead. //

By itself, this warning doesn’t mean there’s a problem with MtoA or Arnold. The warning means that the MtoA plugin isn’t loaded, so all you have to do is load MtoA:

1. Click Windows > Settings/Preferences > Plug-in Manager
2. Scroll down until you see mtoa.mll
   
3. Click the Loaded and Auto load check boxes.

However, if you get a “Unable to dynamically load : ../mtoa.mll The specified module could not be found.” error, then that’s a different problem.