Help required please!!

I have saved an acb file on my USB stick when working on a different computer which had a newer version of atlas-ti, where you don't have to convert your word docs to rtf, but can upload them as docs.
Now I am trying to upload i.e. unbundle this file into an older version of atlas ti (version 5.2 where you still have to convert your word docs to rtf) and it states that there is a conversion error (I presume this is due to the rtf/doc difference but i might be wrong here) Does anybody know how to deal with this?? It is quite important for me because I can't access the other computer with the new version anymore.

Many thanks in advance,