Unhandle exception in KeyPress

Hi all,

The following is a unhandle exception report:
************** Exception Text **************
System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
at System.Collections.ArrayList.get_Item(Int32 index)
at ActiproSoftware.SyntaxEditor.SyntaxEditor.a(EditorView A_0, Keys A_1, Char A_2, Boolean A_3)
at ActiproSoftware.SyntaxEditor.SyntaxEditor.OnKeyPress(KeyPressEventArgs e)
at Agilent.Vee.UIControls.DotNetFormulaBox.OnKeyPress(KeyPressEventArgs e)
at System.Windows.Forms.Control.ProcessKeyEventArgs(Message& m)
at System.Windows.Forms.Control.ProcessKeyMessage(Message& m)
at System.Windows.Forms.Control.WmKeyChar(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
at ActiproSoftware.SyntaxEditor.SyntaxEditor.WndProc(Message& m)
at Agilent.Vee.UIControls.DotNetFormulaBox.WndProc(Message& message)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

DotNetFormulaBox is a sub class of SyntaxEditor and its OnKeyPress call base.OnKeyPress(e) firstly;
When I am debugging, I find that KeyPressEventArgs e is a SPACE. And the exception is random. :(
Could you give me some advice?
Thanks in advance.
DeepNight

[Modified at 12/12/2006 11:58 PM]