Are these Word documents created in Word 2007 (They will have an extension of .docx if they are)? You might need this from Microsoft to the read newer format to be read by an older system.
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Could you please make these users access their emails on another PCs with the same Lotus Notes & MS word version .then check if still they have the same problem or not ....
By the way I recommend to uninstall MS word and make a fresh installation on these two users then check it out .