This may not be your situation, but it might help others with
similar problems...
We have had this happen before on our intranet. The problem
was that the person who installed CF allowed the CF service to log
in using HIS username and password. As a result, CF had access to
everything the installer had access to.
Following good network security practices, the installers
network password expires every 45 days or something like that.
Note, however, that the permissions problems did NOT coincide with
the expiration of the installers password, so people were stumped.
As it turned out, the login username and password are not
validated until the NEXT TIME the CF service is stopped and
started. Thus, the problem did not rear it's head until there was a
need to restart the server. This happened to be about a month after
the installers password actually expired.
As I said, this is not exactly the same as your problem, but
it could be a username/password issue nonetheless, preventing the
username and password combination of the CF service from 'seeing'
the directory in question.