I have written an AddIn (call it AddIn_2) which picks up where another
(AddIn_1) leaves off.

AddIn_2 uses events to identify when a particular worksheet is
activated to enable a menu item.

AddIn_1 creates that worksheet and reiteratively activates it during
its process ... causing a messy crash. AddIn_1 is a commercial product
and I have no access to its code.

I want to be able to write a clause like
if AddIn_1 is running

end if