ASP.net Exception - Object reference not set to an instance of an object.

Object reference not set to an instance of an object

Possible cause : 
You are trying to assign value to a null object.
You are trying to get value from a null object.

How to detect:
Assignment statements  => Debug and check if the left hand side objects used in the assignment is null.
Accessing value related statements => Check if the objects used in the statement is null.