Error message: Object reference not set to an instance of an object
Have you included a class int he file but forgotten to create it as an object?
private SomeClassName SomeClassName1;
public PageVentilationKeyPopup(string PopupType, int LevelNumber)
{
this.InitializeComponent();
SomeClassName1 = new SomeClassName(); //<Did you forget this?Feel free to comment if you can add help to this page or point out issues and solutions you have found. I do not provide support on this site, if you need help with a problem head over to stack overflow.