Global.asa changes ignored

I am trying to move some working ASP code onto a new shared host running
IIS5.
Things were going fine but now it seems to be ignoring changes to
global.asa; for example I reduced it to just this -
sub Session_OnStart
session("adwt")="??????"
end sub
and was not able to find a value for the session variable in a script,
although I was able to set it there and then read it next call.
Any thoughts please?
The only area I haven't worked with before is load-balancing - could that
affect things.
Thanks in advance for any suggestions.
Peter Croft