I use a small chunk of VBA to allow me to edit summary properties via
an Excel sheet. Basically, one macro retrieves a list of file names
from a folder, then list those names and various properties in a sheet
(properties include Title, Author, Subject, Category, etc.)

I have a second macro that changes the values of those properties if
they've been edited in the Excel file. Occasionally, I run into a
permission error when trying to update certain properties. It seems to
be localized to situations where the property's previous value was null
and I'm trying to change that value. If I use Windows Explorer to
change the value and then try to edit via my macro, it will work fine.

For some fields, like Title, I can remove a value and then use the
macro to add one without a problem. With other fields, like Category,
I'll get the error anytime I try to update it from null to something.

Any guidance would be appreciated. I've searched high and low and
can't seem to figure out what is happening.

- John