Performance issues occur when Windows Rights Management Services client has very large files associated with an RMS policy
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.
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB970887.