Null reference exception

The result of that specific piece of code could return a null value or a variable is not initialized, but it could also never happen or result in any trouble. The compiler just noticed that there is a condition where it could happen and it isn't surrounded with a try..catch to fix that or a variable isn't assigned a value, like String s = "". You could simply check it, try and see what happens.

Good luck!

I think you did not get a clear answer so far.

Simply run you code under debugger; it should point you to the line of code where it happens. The reason is only one: the code tries to access an instance of an object which is null, no matter by what reason. When you find it, check the offending object for null and act appropriately under the if block. What to do in the object is null totally depends on your semantic; only you can decide what to do.

Alternatively, catch all exceptions on top of each thread and dump exception with its stack using System.Exception.Stack. In Debug configuration, it will show you all the code line numbers where bad thing happens.

[EDIT]
If you have warning, it does not mean you can catch exception in all cases. Make sure there is no warnings. A warning shows you exact location of the line where an initialized variable is used. Never allow such situation. Initialize all the variables before use; no exceptions.

—SA