Can't Book Resource from Public Calendar

[Ben]

Hi,

We have a number of resources, (training room, meeting room, projector etc)
setup as mailboxes on Exchange 2003, this allows us to schedule the resource
for meetings, so that other uses can see its booked, and get warnings if
they try to book it at the same time. This works fine for all of our users
when they book out the resources from their calendars.

However, we have a public training calendar (under all public folders), that
anyone can book training events for, but if we try to book one of the
resources, we get the following error:

"The operation failed. An object could not be found. Unable to directly book
a resource for this meeting."

Apparently this means that we do not have access to directly book an
Exchange resource, I assume this means the Public Calendar does not have
access, seeing as the actual user who's booking it, does have access, and
can book it from their own calendar.

So, is there a way to give a public calendar access to schedule resources?
I've set the resources permissions for Default & Anonymous to Author, but
still the error occurs, what permissions need to be set?

Many thanks

Ben