I got Docs to Go free on my T600 like a year ago, but recently it isn't working.

after I download an attachment, even a simple word document, and click on it, a dialogue box comes up that says, Application Missing - the application to open this type of document could not be found!

of course on my laptop its a simple word document, easy to open. Why won't Docs to Go do it? has the free version expired? I haven't changed treos, or email software (treo mail), at all of late, so I can't figure out what's causing this.... any help or advice would be appreciated...