If you move the Render Appearance Library from its default location, use the Rendering tab of the to specify its new location.
The Render Appearance Library is a read-only library that stores all render appearances for materials, the default RPC content provided with the software, and related rendering information.
When you install Revit Architecture, this library resides in the following default location:
C:\Program Files\<product name and version>\Data\Rendering\assetlibrary_base.fbx
If necessary, you can move the Rendering folder and its contents to another location, such as a second local hard disk or a partition on a local disk. After moving the Rendering folder, update the Render Appearance Library Location to point to the new location of assetlibrary_base.fbx.