Without more information, I've afraid I don't have any guesses as to what might be causing this.

Is there any more information? Is there a call stack?

When you say "loading my form", do you mean in the designer in Visual Studio or when you run the application? If it's at run-time, then you might want to try setting the IDE to break on all run-time exceptions. Sometimes exceptions like this are occur inside event handlers and so the exception gets caught and then bubbles up so the line of code that you get the error on is not actually where the real exception occurred.