It worked at first. I went in and made the changes you suggested and saved
the file and closed Word. I opened up my merge and it let me through to the
"Merge to Document" dialog box, and then the "Select Filename Field" dialog
box. I selected the last name field, browsed and found my file path and
clicked Continue. I then receive the following VB error message:

Run-time error '-2147467259 (80004005)':
Method "PrivateProfileString' of object 'System' failed

The error dialog box has four option buttons, Continue, End, Debug, and
Help. Continue and Debug are both grayed out and not available, End and Help
are the only options available. The help screen it brings up is only gray,
no info. When I click end, it just completes the normal merge, all in one
document.

I'll wait for you to email me the revised add-in, or I'll check back on
Graham's site later to see if it has been uploaded. I'll let you know how
the new version works.