Fatal error on upgrade? : Fatal error: Cannot redeclare class MarketPress_Shopping_Cart in /home/br

ok - paid member downloaded directly the full version of marketpress tried to upgrade to pro on barriertape.org and I get :
Fatal error: Cannot redeclare class MarketPress_Shopping_Cart in /home/brickshi/public_html/barriertape.org/wp-content/plugins/marketpress/marketpress.php on line 7086

any ideas??

Regards

Matt