If you log in to DNP as "serveradmin", click Edit Details on the right under servereadmin summary, remove the tick "Ecommerce Enabled", and press the update button to save the change, the Ecommerce is still enabled.
I also tried changing the serveradmin last name when removing the tick to see if it remembered that, and it didn't do that either so it isn't just a problem with the tickbox.
I'm on a new trial install running DNP v2.8.1, Win2003 Std SP2, and tried btoh Firefox 3 + IE7
HTH, Rupert