HI,
I don't know if this will help you or not, but my HP drive came with a package called "CD Diagnose". It has a bunch of advance things like: "Recover Track" which tries to recover the last track on a CD if it was damaged. It will let you close sessions/tracks. Have a look at all sessions, etc. I'm not sure where you can get this, I seem to remember picking up an updated version from HP's web site at some point in the past.
Are you sure that the session was closed? Was it written with a Packet Writer? If so, are you using UDF software i.e. DirectCD or a UDF Reader?)