Embedded Shipping Estimator broken after installing google checkout

This was working before installing GCO.
Now a message is displayed saying

"Fatal error: Cannot redeclare class order in /home/alifina/ 
 public_html/boutique/includes/classes/order.php on line 1979" 

The estimator still works as a popup.
The embedded estimator works if GCO is disabled.

I'm running ZenCart v1.3.7 and GCO 1.4alpha

Is there no one who has experienced this?
I really like the estimator embedded because some browser are set to block popups or display them in a tab.

Can anyone know if this is really related to the GoogleCheckout module?

Thanks for any help or comments.

This problem still persists. I was hopeful that it would go away after fixing my shipping zone problem, but it didn't.

Can anyone shed light on this problem?

thanks

I don't know what happened but this started working again.
Strange, huh?