[Plugin: Events Manager] Event Manager update conflicts with PHPurchase widget

I have updated Events Manager and it now causes problems with PHPurchase cart widget. Here is the error message:

Fatal error: PHPurchaseCartWidget::widget() [<a href='phpurchasecartwidget.widget'>phpurchasecartwidget.widget</a>]: The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "PHPurchaseCart" of the object you are trying to operate on was loaded _before_ unserialize() gets called or provide a __autoload() function to load the class definition in /home/public_html/wp-content/plugins/phpurchase/cart-widget.php on line 15

http://ww.wp.xz.cn/extend/plugins/events-manager/