AutoCAD for Mac and AutoCAD LT for Mac versions 2016, 2015, and 2014 are compatible with Mac OSX v10.11 (El Capitan), but are not designed to run on the Sierra. For the official word from Autodesk read this: AutoCAD and Apple MacOS Sierra (10.12) what you need to know.
The only workaround appears to roll back to the supported operating system.
UPDATE: There was an update released shortly after this blog was written that resolves this issue. However, this update is only for AutoCAD 2016 for the Mac: AutoCAD 2016 for Mac Update 4 and AutoCAD LT 2016 for Mac Update 4. For 2015 and previous versions the above workaround is still the only solutions.