Your installation of Office is behind on updates. While I don't think this particular problem is completely fixed in the latest update, I know that some people reported that the problem was resolved by updating to 15.24. For others, there was no improvement.
I suggest updating, then going to Word Preferences and making sure there is a location set for the AutoRecover file. Setting the location of the AutoRecover file has solved this issue for some, but not all users.
Word Preferences > Personal Settings > File Locations
Follow these instructions for updating your Office installation:
Make sure your Mac has a working internet connection before checking for updates. Install Mac OS X updates followed by Office updates.
Mac OS X updates:
To get Mac OS updates, go to the App store on your dock, and then click the Updates button to reveal available updates.
Office Updates
To get the update:
- Open any Office application:
- Make sure your Mac has a working internet connection
- Go to the Help menu and choose Check for Updates
- Let AutoUpdate check for and install updates
- Restart your Mac
If you want to be extra diligent, when you do that final restart, you might try doing a
Safe Boot because you are using El Capitan (also applies to Sierra). In these two editions of Mac OS doing a safe boot runs Disk Utility and fixes any directory problems you might have but
be unaware of. It certainly can't hurt to do this, and there's a small possibility that doing so could fix the trouble we're aiming to solve. Once you've performed the Safe Boot and tested there, you can do a regular restart and test again. Please reply as
to whether or not any of this fixes the problem. Thanks.