User-744022866 posted
Basically dll file is a compled code file. So couple of days before the code you accessed was working, but now it is throwing error. You need to analyze the code and see what is causing the error.
Lot of things can cause the above specified error. For e.g. if your code accessing a particular key from session and if it is not available this error can happen. To identify the error you need to look in to the source code.