Hi Russell

We can put this to rest at the moment, especial now that I/we can see what happened.
At the present, everything if working as expected, it ain't broke any more...

Sequence of events so you can see how this cluster all came about:
Migrated to different server
Working on a partial clone from elsographics going to 1nhmugs
Was getting several error notices from elsographics, not uncommon for a user to trigger an error page, but enough for me to double check my forms for proper function. This is when I noticed that hitting the back was resulting in "cannot_return" error The top page index is <undefined>" which sent me on a search of your forum for a quick fix so I could get back to my cloning.
Did the recommendation as specified which fixed this problem.

Testing of my clone project, is when I began seeing an occasional "insession specified, but no data found in session" when trying to trigger my error page. Initially it seemed random, but after finding a way to duplicate it, it appeared to cache related.

Talking to both you and the server people, having them double check the php etc, they suggested it might be due to the current version of php 5.3 and it would be no problem to roll it back to 5.2*.* and no trouble if I later wanted to go back (I guess php is an easy/quick up/downgrade)

I am now back with my older known working version of FM (8.23) and the known compatible php 5.2*. We are back at square one, which is where I wanted to remain in the first place.

I am happy with my current version of FM, it does all I need for now. I don't understand enough about Ajax or other features which I am sure would be useful if and when I venture to understand them

Thank you