Method 'Add' of of object 'IAcadSelectionSets' failed

I get the error:

Method 'Add' of of object 'IAcadSelectionSets' failed

at the Set ssText... line in the VBA code below when the previous selection
set contains text using a TrueType font.
It works fine if the previous selection set uses shx fonts. Any ideas?
The previous selection set is created in a lisp routine using

(if (> (sslength qa_ssgroup) 0)
(progn
(command "select" qa_ssgroup "")
(vl-vbarun "modTextNoteEditorSelectPrev.TextNoteEditorSelectPrev")
)
)

----------------------------------------------------------------------------
-------------

SelectText:
Err.Clear
Set ssText = ThisDrawing.SelectionSets.Add(Now)
If Err.Number <> 0 Then
' MsgBox "Sorry, but an error occured when selecting this item." & vbCrLf
& _
"Try editing this object with the DDE command instead.", _
vbOKOnly, "Selection Error:"
Exit Sub
End If

' Add objects to the selection set
ssText.Select acSelectionSetPrevious, , , vDxfCode, vDxfValue

 

Never mind, it was my lisp routine that overfilled the available selection
sets.