CANNOT CONNECT - ERROR

MV

I have the latest version of Teamviewer and am able to connect with 2 other computers. However, another connection in India (I'm in the U.S.) cannot connect to my computer. He was able to connect once, yesterday, but not since then. He has the latest version of Teamviewer. Here is a screenshot of the error message: http://prntscr.com/h28j6t

It says 'reason unknown'. What is the solution?