C# Edit and Continue: error 4009 

Error Message

Updating a [using alias | field | event | fixed size buffer | constant | attribute] will prevent the debug session from continuing while Edit and Continue is enabled

This error indicates that you tried to modify a using alias, field initializer, attribute target, or attribute arguments.

Consider the following example code:

class Program

{

   private int Example = 10;

   static void Main() { }

}

If you step into the application, then try to change the Example = 10 to Example = 20, the error occurs.

To correct this error

• Undo the changes, then continue debugging without the changes

  -or-

  On the Debug menu, click Stop Debugging, make the changes, then start a new debugging session.

See Also

Reference

event (C# Reference)
using (C# Reference)
Supported Code Changes (C#)
Edit and Continue (Visual C#)

Other Resources

Edit and Continue Errors and Warnings (C#)