Access to the interpretations and teachers' notes sections is restricted. Authenticated users get values placed into session variables which are then checked on the relevent pages. For some reason, on the new server those values cannot be read from the session array. It did not appear that the subsequent pages started a new session (looked up the php reference on that and no files were created in the sessions dir), just that they couldn't read the values in the session variable. Nor did it appear that the problem resulted from different servers in the cluster writing to different temp or session dirs. Ryan checked on that for me.
I ended up passing the SID explicitly in the URL as a GET argument, and even though the subsequent pages make no use of that GET argument, the session array values are now available. So, it now works, but we're not sure why.