Hi Cindy,
thank you for your answer. I take it you mean that my code (which is a
C++ application working with Word2003) should use explicitly DDE.
Actually, the application currently works with the following Connection
string (the 12th argument passed to the OpenDataSource method):

"Provider=Microsoft.Jet.OLEDB.4.0;User ID=Admin;Data Source=" +
sDataSourcePath + ";Mode=Read;Extended
Properties=\"HDR=YES;IMEX=1;\";Jet OLEDB:Engine Type=35"

while, if I understand what you said, I should replace the use of Jet
OLEDB with the use of DDE. Is it correct?
But I have two questions:
1) why does the current application works with most of the mailmerge
documents submitted to it?
2) why doesn't it work with only some othe documents?

Thank you
Alessio