The client is throwing an error. A real fix would be you'd have to figure out which model is screwing it up.
The first thing to do, is to go to the console, and see which line the error is coming from. In that method, put a try { and catch(Exception e) e.printStackTrace() } around the code, and then it won't occur again.
To have a full fix, figure out which model is causing the problem. Start at the error thrown from the e.printstacktrace() :-)!