The file Xceed.Wpf.Toolkit.dll must be in same place as the program.
Try copy the file Xceed.Wpf.Toolkit.dll to same directory as Gantt.exe.
The file Xceed.Wpf.Toolkit.dll must be in same place as the program.
Try copy the file Xceed.Wpf.Toolkit.dll to same directory as Gantt.exe.