I had similar issues, and this fix depends on how you've got it set up.
My issue was that I did not have an Internet MIME type set up to handle .vfb
files.
Here's how my setup goes:
Users publish their IFB info to a web site in Outlook to:
http://mydomain.com/freebusy/FirstLast.vfb
In the contact card on the "Details" tab that same URL is referenced in the
Internet free-busy address field.
I had to launch IIS admin for the server that hosted the
http://mydomian.com/freebusy virtual server, went to HTTP Headers tab and
added a mime type for extension ".vfb" and content type "text/calendar"
Voila! Free/Busy info populated on a remote system for that user.
Before going through the hassle of setting this up, you can test if this is
your problem by doing this:
throw the url to your users .vfb file into an internet browser, if you get a
404 then you need to add the MIME type, if you are prompted to download an
iCalendar file then your MIME type is configured properly and you've got
anothe problem. (more than likely a permissions problem on the ACL for the
file system location where your IFB info is stored or no anonymous access
allowed on the IIS VS)
