Bad news. It still fails over a lot of combinations and repeats of DoEvents and delay loops as suggested (anything from 1,000 to 10.000,000). But it still works when stepped into with the debugger.

I know what you mean about sandboxing. I've come across that with accessing external files but I don't see how it might have its tentacles in here as the instruction does work, albeit manually the first time, and as designed for subsequent executions with no further intervention.

Thank you for taking the time to think about this for me.