Which version of Word?

What if you try going through the process of connecting to the Excel data
source again?

With your mail merge main document open, can you open up the VBA Editor,
open up the Immediate Window, type the following commands, and post the
results here?

print activedocument.mailmerge.datasource.name
print activedocument.mailmerge.datasource.querystring

(don't bother with the next one if you're using Word 2002)
print activedocument.mailmerge.datasource.connectstring

If you can't do that, can you
a. open your mail merge main document
b. save it in HTML format
c. close it, and re-open it in Notepad
d. look down the file for keywords that refer to mailmerge (they are
usually near the top of the file)
e. try to identify the name, query and connect info and paste it here (the
mailmerge stuff is usually followed by a long list of rather short rows
which you need not copy/paste here).

Peter Jamieson