Asp.net MVC 4: Jquery Ajax status 12031

Problem:

This morning I got message that deployed website is not working.
After checking it out. I got ajax error, when I was loading particular method ex: GetJsonData(). All other methods did work fine.

Small investigation lead me to ActionResult.

so it was

Solution:

public ActionResult GetJsonData()
{
  var result = ...
  return Json(result);
}

change it to


public JsonResult GetJsonData()
{
  var result = ...
  return Json(result);
}


and promlem was solved. Next time always return correct result. )

Server error 500 using dotless

  Problem:
  Today website using less files failed to compile by dotless. It returned server error 500.

  Solution:
  Problem was in application pool.
  "Managed Pipeline Mode" used by site was "Classic" change it to "Integrated"