See the article "Creating a Mail Merge Data Source" at:
http://www.word.mvps.org/FAQs/MailMerge/CreateADataSource.htm
and
See the article "How to create a Mail Merge" at:
http://www.word.mvps.org/FAQs/MailMerge/CreateAMailMerge.htm
If you can't see what you have done is causing the problem, post back with
the names of the merge fields in the data source, exactly as they are
entered into that file.

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Hope this helps.
Please reply to the newsgroup unless you wish to avail yourself of my
services on a paid consulting basis.
Doug Robbins - Word MVP
>I have completed my data source but when I open my letter and try to merge
> the data source I get an "invalid merge field" and it won't merge into the
> letter. what have I done wrong and how can it be fixed.