If the images you are referencing don’t exist while using an Infragistics WebImageButton (Version 10.1.20101.1011) HttpContext.Current.Session will return null dropping your session.
wibAddComment.Appearance.Url = "../App_Themes/EHAP Theme/images/Comments/FileDoesntExist.gif"; wibAddComment.HoverAppearance.Url = "../App_Themes/EHAP Theme/images/Comments/FileDoesntExist.gif"; wibAddComment.PressedAppearance.Url = "../App_Themes/EHAP Theme/images/Comments/FileDoesntExist.gif";