At a guess I'd say Norton is picking up on exactly that point. Yes its great you've used a unique identifier, no Norton doesn't know anything about it, so doesn't no how to react. What should an arbretary piece of software do about a file system wuth an unknown unique identifier? My gut feeling is to treat a unique identifier as if it were apple, unless you know something (ie say symantec started doing stuff, I bet they have a number norton knows about). If Norton haven't implemented it this way, then you'll have to either ignore the error, if you can, (which would be my preference) or lie to norton about who last made changes to the drive. The later would work, but if there are errors in your implementation there is no way for other clever utilities to identify whats yours and whats not.
In short, if you really have to, change the value to something that works quietly.
Simon