As a programmer myself, I know saying "there's an error" isn't helpful, so here's a transcript of the error message:
Code: Select all
Error in ProcessCmdKey
System.InvalidOperationException: Operation is not valid due to the current state of the object.
at Sudoku.Cell.SetValue(Digit NewDigit, CellStatus NewStatus, UserMove um
at Sudoku.Effect.Undo()
at Sudoku.UserMove.Undo()
at Sudoku.Grid.Undo()
at Sudoku.Form1.MenuUndo_Click(Object Sender, EventArgs e)
at System.Windows.Forms.MenuItem.OnClick(EventArgs e)
at System.Windows.Forms.MenuItem.ShortcutClick()
at System.Windows.Forms.Menu.ProcessCmdKey(Message& msg, Keys keyData)
at System.Windows.Forms.Form.ProcessCmdKey(Message& msg, Keys keyData)
at Sudoku.Form1.ProcessCmdKey(Message& msg, Keys keyData)