With the same issue, I tried both fixes on this thread and still had no luck. I thought it might be an issue with spaces in the path name.
I tried quotes; sometimes that fixes this issue.
Nope. Same problem. So I tried moving everything. I moved the entire "arduino" folder from the path noted previously up one level and changed the preferences.txt file to match.
Things loaded up just beautifully. When opening a sketch, the dialog started in the wrong folder, but I was able to navigate where I needed to go and upload sketches to my Uno. I still don't know for sure if the space was the problem, but I got my stuff running.
I hope this helps someone!