I have an AddIn into which are written a few small details before
close (I know this isn't great practice but it saves me having to
setup a log file external to the AddIn and the attendant risk that
this will be deleted)

When a second instance of excel is opened it opens the AddIn as read-
only. On shut down this prevents the few small details being written
back to it and the user is prompted to save a copy of the AddIn
elsewhere. Undesirable

Two solutions come to mind (beyond setting up a remote log file) but I
don't know how to effect either
1. prevent the second instance of excel from opening the AddIn
(preferable)
2. prevent the addin from working in the second instance, hence not
generating the few small details and not being able to save them

How can I get the second instance of excel NOT to load the addin?
Thanks in advance ... and thanks to all for all the databased
contributions here ... if this group wasn't here I'd still be spending
all afternoon charting data instead of doing it at the touch of a
button!
Matthew