Thanks for that tip - I will use it.
I think I have found the xause of the problem - it appears that only pages which have some SA access rule on store the session variable - though this seems a bit bizarre to me! I had created a recordset where MemID = the Session variable and no record was found. However, when I applied the page access rules, it worked! Perhaps one of those little idiosynchracies that I'll have to learn.