100+ Questions and counting!
Delivering bug free code is part of your job, may be it is time to learn how to track down bugs by yourself.
The error message is the result of a unique combination of your code, SQL server configuration, database ... that nobody can reproduce. You are the only one able to find the problem and correct it.
Quote:
NullReferenceException: Object reference not set to an instance of an object.
All we can say is that somewhere, an operation that return an object fails and the error message pops when you try to use that failed answer.
Use the debugger to see what your code is really doing.
Your code do not behave the way you expect, or you don't understand why !
There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your code is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.
Debugger - Wikipedia, the free encyclopedia[
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Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[
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Basic Debugging with Visual Studio 2010 - YouTube[
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The debugger is here to only show you what your code is doing and your task is to compare with what it should do.