I'm having exactly the same problem. Mahjong isn't working since this morning. I open the program and it says there is a download error and it asks me if I want to play offline. Retry doesn't work. If I do say play offline, it logs me in, but I get more download errors when I try to access daily challenges. I tried repair, didn't work.
I tried to reset, didn't work.
Just uninstalled and reinstalled, didn't work.