Disabling CTRL-X shortcut in Visio 2003 Addon fails

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Hi,
I'm trying to disabling the "Cut" (CTRL-X) shortcut in a Visio 2003 addon
written in C#; however it doesn't works.

I rewrote this VBA Code:

Visio2000: How to Bind a Custom Accelerator Key for a Custom Menu to a
Specific Drawing Window
http://support.microsoft.com/?scid=kb%3Ben-us%3B281504&x=7&y=17

into C#:

Visio.UIObject visioUI = null;
if (VisioDocument.CustomMenus == null)
visioUI = CExeAddon.VisioApp.BuiltInMenus;
else
visioUI = VisioDocument.CustomMenus;

Visio.AccelTableClass vsoAccelTable =
(Visio.AccelTableClass)visioUI.AccelTables.get_ItemAtID(drawingMenuId);
Visio.AccelItemsClass vsoAccelItems =
(Visio.AccelItemsClass)vsoAccelTable.AccelItems;
Visio.AccelItemClass vsoAccelItem;

//This fails
//IEnumerator AccelEnum = vsoAccelItems.GetEnumerator();

// GetEnumerator() has two overrides, so, I tried both of them:

//This fails
//IEnumerator AccelEnum = ((Visio.IVAccelItems)vsoAccelItems).GetEnumerator();

//And this as well
IEnumerator AccelEnum = ((IEnumerable)vsoAccelItems).GetEnumerator();

while (AccelEnum.MoveNext())
{
vsoAccelItem = (Visio.AccelItemClass)AccelEnum.Current;
if (vsoAccelItem.CmdNum == (short)Visio.VisUICmds.visCmdUFEditCut)
{
vsoAccelItem.Delete();
break;
}
}

VisioDocument.SetCustomMenus(visioUI);

It should work; however, I'm getting the following exception as soon as the
GetEnumerator() method is called:

System.InvalidCastException: QI for IEnumVARIANT failed on the unmanaged
server.
at
System.Runtime.InteropServices.CustomMarshalers.EnumeratorToEnumVariantMarshaler.MarshalNativeToManaged(IntPtr pNativeData)
at Microsoft.Office.Interop.Visio.AccelItemsClass.GetEnumerator()

How should I do this in C#?

Thanks in advanced.

Best regards
Josef
.