The NullReference Exception for Visual Basic is no different from the one in C#. After all, they are both reporting the same exception defined in the .NET Framework which they both use. Causes unique to Visual Basic are rare (perhaps only one).
This answer will use Visual Basic terms, syntax and context. The examples used come from a large number of past Stack Overflow questions. This is to maximize relevance by using the kinds of situations often seen in posts. A bit more explanation is also provided for those who might need it. An example similar to yours is very likely listed here.
Note:
This is concept-based: there is no code for you to paste into your project. It is intended to help you understand what causes a NullReferenceException (NRE), how to find it, how to fix it, and how to avoid it. An NRE can be caused many ways so this is unlikely to be your sole encounter.
The examples (from Stack Overflow posts) do not always show the best way to do something in the first place.
Typically, the simplest remedy is used.
Basic Meaning
The message "Object not set to instance of Object" means you are trying to use an object which has not been initialized. This boils down to one of these:
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
Finding The Cause
Since the problem is an object reference which is Nothing, the answer is to examine them to find out which one. Then determine why it is not initialized. Hold the mouse over the various variables and Visual Studio (VS) will show their values - the culprit will be Nothing.
IDE debug display
You should also remove any Try/Catch blocks from the relevant code, especially ones where there is nothing in the Catch block. This will cause your code to crash when it tries to use an object which is Nothing. This is what you want, because it will identify the exact location of the problem, and allow you to identify the object causing it.
A MsgBox in the Catch which displays Error while... will be of little help. This method also leads to very bad Stack Overflow questions, because the you can't describe the actual exception, the object involved or even the line of code where it happens.
You can also use the Locals Window (Debug -> Windows -> Locals) to examine your objects.
Once you know what and where the problem is, it is usually fairly easy to fix and faster than posting a new question.
