DAW,
Got this message today while debugging / closing a DF19.1 program
And I can replicate it again and again and again ... you need at least 4-5 views open with some dbCJGrids, then using the menu: File->Exit
Entering the "debugger limited break mode" - it seems to be at the "Page_Delete" procedure within the DFLabel_Mixin class.
But always on a different object (i.e. dbform)