I would probably open up a case with Microsoft, see if there is a bug with rollup 3. They pulled the original rollup 3 and re-released it due to some issues with it.
One thought, do all users see this error, or just some? One thing that some people may not know is that you cannot create appointments in CRM 3.0 unless you have read access to the service calendar (even if you do not use the service calendar).