A Windows Vista-based client of the Windows Rights Management Services (RMS) generates a new content key every time content is published. You cannot reuse the original symmetric key (content key) when you republish a piece of content.
If the RMS policy setting is changed to Add, a new user, a new group, or a new content key is generated, and the original file has to be re-encrypted again. This behavior causes performance issues for the applications that use large files. This problem occurs when the RMS client has very large files associated with an RMS policy.