The application is in break mode - Unable to determine cause

In one of my web applications I had the same issue, to find out what was wrong,after searching for similar issues, most suggested changing my debugging options. So in the debugging options, under general, I marked the second option "Break all processes when one process breaks" and nearly at the bottom, "Enable native Edit and Continue"; "Apply changes and Continue".

With this, my app finally stopped where I had the issue (Illegal characters in a string which ajax did not like) and was able to evaluate the values and find out what was wrong, edit the code on the go till it worked. Here's a screenshot of my debugger options. Hope you catch your bug:)

Debugger options

You may not be able to see the code where the exception happens if it's a part of a library or something else not written by you. The following might help:

Debug > Options > General > Uncheck "Enable Just My Code"