Holy cow, I wrote a book!
much speculation as to
how the "Ignore other applications that use Dynamic Data Exchange"
setting got set.
is that somebody
used global state to manage a local problem.
"Why on earth does this setting exist?"
I don't know, but there appear to be scripts which rely on it.
The setting is exposed to scripts,
and perhaps at some point you ran a script
which didn't want
Excel to be interrupted while it was running.
The documentation for the
Excel Application Object
does say that it contains application-wide (global) settings.
I'm not saying that's why you are encountering the problem,
but it's just one possibility I ran across while doing some
Web searching to learn more about the setting.
One of those Web searches took me to
Susan Bradley (the SBS Diva)
one reason why somebody would enable this checkbox:
It shuts up a different warning.