Specified argument was out of the range of valid values' error (editor)

[arj0n]

As I can't seem to find the Bug and Suggestion Tracker and the link in the FAQ (https://www.adventuregamestudio.co.uk/forums/index.php?action=projects) isn't working, I hope it's ok to post it here:

I had a couple of tabs (room and a few scripts) open in AGS (Build 3.5.1.11)
When I selected 'close all tabs' an 'Specified argument was out of the range of valid values' error popped up (see below)
A red cross was shown over the whole area where normally the tab names are present.

Code: ags

Error: Specified argument was out of the range of valid values.
Version: AGS 3.5.1.11

System.ArgumentOutOfRangeException: Specified argument was out of the range of valid values.
   at WeifenLuo.WinFormsUI.Docking.DockContentCollection.GetVisibleContent(Int32 index)
   at WeifenLuo.WinFormsUI.Docking.DockContentCollection.get_Item(Int32 index)
   at WeifenLuo.WinFormsUI.Docking.DockPaneStripBase.TabCollection.get_Item(Int32 index)
   at WeifenLuo.WinFormsUI.Docking.VS2005DockPaneStrip.EnsureDocumentTabVisible(IDockContent content, Boolean repaint)
   at WeifenLuo.WinFormsUI.Docking.VS2005DockPaneStrip.OnPaint(PaintEventArgs e)
   at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer)
   at System.Windows.Forms.Control.WmPaint(Message& m)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at WeifenLuo.WinFormsUI.Docking.DockPaneStripBase.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)