if the name of the session being created by your login system is SecurityAssist_UserID, then yes, you will need to change my example code and substitute "SecurityAssist_UserID" instead of "UserID"
this now works fine. thanks for your help :)
though back to the original topic about the postage. it still is not working. it is not showing up in my checkout for postage.
to correct what i need i actually need it to have
$8.50 for postage to VICTORIA, TASMANIA,QUEENSLAND,NEW SOUTH WHALES and SOUTH AUSTRALIA
$15.50 postage to WESTERN AUSTRLAIA
and FREE POSTAGE to Canberra.
can you please take a look?