I ran across a problem this morning getting into the Public Folders node in Exchange System Manager on a Small Business Server 2003 machine. Everytime I would try to access this node I would receive the message:

80090308 "The token supplied to the function is not valid"

A bit frustrating. The MSKB suggested turning off the SSL requirement for the Exadmin virtual directory in IIS, but that alone did not solve the issue. I ended up finding a blog post that gave instructions for changing a value in ADSIEdit, which did the trick!

http://blogs.technet.com/petergal/archive/2006/05/12/428152.aspx