Error messages ( 1605) when running Thesaurus

[Gene]

I get a bunch of messages saying that Microsoft Office
Word cannot open the thesaurus because the installer could
not install the necessary files due to installer error
1605. This message pops up four times after you click OK,
but then the thesaurus does actually load, although the
highlighted word is not automatically plugged in search
box. If your enter a word into the search box things work
ok until you load Word again. Any ideas?
Gene