Quote: I checked the manual for the camera and it says to use circular instead of linear polarisers. Something to do with the way the TTL metering system works.
Indeed. It's got nothing whatsoever to do with if the camera is film or digital, purely with the way it gathers light for the AF and/or metering systems. Systems that use beam splitters/semi-silvered mirrors can be confused by linear polarisers - that's virtually all AF SLRs, film or digital, and many other SLRs with spotemeters or multi-pattern meters. Some people report success using linear polarisers with such cameras, but I wouldn't personally take the risk. A polariser will act as an ND filter, but you could consider a non-graduated ND filter.