Hello, I was trying to do a ShowMenu and then switch with the results when everything just....somehow...broke?

The error is:
System.Exception: Starting transaction when previous transaction not finished
at TextAdventures.Quest.UndoLogger.StartTransaction(String command)
at TextAdventures.Quest.EditorController.DeleteElement(String elementKey, Boolean useTransaction)
at TextAdventures.Quest.Editor.Delete()
at TextAdventures.Quest.MainToolbar.HandleClick(String tag)
at TextAdventures.Quest.MainToolbar.HandleClick(Object sender, EventArgs e)
at System.Windows.Forms.ToolStripItem.RaiseEvent(Object key, EventArgs e)
at System.Windows.Forms.ToolStripButton.OnClick(EventArgs e)
at System.Windows.Forms.ToolStripItem.HandleClick(EventArgs e)
at System.Windows.Forms.ToolStripItem.HandleMouseUp(MouseEventArgs e)
at System.Windows.Forms.ToolStripItem.FireEventInteractive(EventArgs e, ToolStripItemEventType met)
at System.Windows.Forms.ToolStripItem.FireEvent(EventArgs e, ToolStripItemEventType met)
at System.Windows.Forms.ToolStrip.OnMouseUp(MouseEventArgs mea)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
at System.Windows.Forms.ToolStrip.WndProc(Message& m)
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)

Look through your code for a typo...
It looks like you added something that just blew Quest's mind...
So that now, everything it offset...
It could be as simple as a missing space... or an extra one.

I would guess you accidentally double-clicked a button; or some other program was slowing the computer down.

That error appears to indicate that you've clicked the "delete" button on an object before Quest has finished processing the last thing you clicked on.

All you can do with that is exit and restart Quest (which I assume you've done by now)