Have you run into a problem in AutoCAD where the Sheet List is empty in Sheet Set Manager?
Autodesk Support has posted about this problem in this article here.
The solution is to fix a problem in the Windows registry at the HKEY_LOCAL_MACHINE\SOFTWARE\Autodesk\ObjectDBX location. In the article there is a download for it. Another solution is reinstall of AutoCAD. Not sure if repair option will fix it or not though.