Yes I deleted and reinstalled both extensions and deleted the cache file.
I now have a working page after starting again and making the eCart server behaviours the last to be added. There is however another problem that I couldn't get round.
I allow users to return from the confirm page to the checkout address page in case they need to correct a mistake in address entry. This return resets the $_SESSION['OrderID'] to 7 on return to the confirm page every time meaning that the checkout success page always points to an invalid record. I got round this by using a different session variable to store an order number to access the record but there is something strange happening with eCart on my system.
Does this make any sense?