The message "Object not set to instance of Object" means that you are trying to use an object which has not been initialized. That is, you either set it to null, or you never set it to anything at all. The runtime throwing a NullReferenceException always means the same thing: you are trying to use a reference. The reference is not initialized (or it was initialized, but is no longer initialized). This points to one of the following:
Your code declared an object variable, but it did not initialize it (create an instance or 'instantiate' it)
Something which your code assumed would initialize an object, did not
Possibly, other code prematurely invalidated an object still in use.
More about....NullPointerException
Walsh