Hi, are you on Linux(with KDE)? If yes, then this "bug" is known. It's not really a bug, the problem is that when a reference to a help topic isn't found theIDE is trying to access it's html version(IIRC), it's a fallback method. But because U++ use xdg-open to open external links if xdg-open is invoked with a bad argument on KDE it show an error message box(in Gnome it's simply ignored, only warnings appear in console if you run theIDE from it).