Please try the following:
private void uc_MouseMove(object sender, MouseEventArgs e)
UserControl dragableusercontrol = sender as UserControl;
if(dragableusercontrol!=null && e .LeftButton == MouseButtonState.Pressed )
DragDrop .DoDragDrop(dragableusercontrol ,
new DropableCanvasDragDropData(dragableusercontrol .Parent as Panel ,
dragableusercontrol ,e.GetPosition (dragableusercontrol )),
uc is just a reference object of UserControl and you are using it as a Type which is not the case. Hence you have to cast it to UserControl type.