Fatal error: Class 'MP_Order' not found after upgrading WD Defender plugin

Hi, I just upgraded WD Defender and am now unable to access my site or the admin site, so I can't deactivate the plugin.

I am getting this error: Fatal error: Class 'MP_Order' not found in /home/earlyart/public_html/wp-content/plugins/marketpresskashflow/_marketpresskashflow.php on line 150.

I have looked on the search but not found anything relating to this.

Please help, I have a lot of work to do on this site today!

Many thanks, Pete