Our site: http://bigbeartools.com
I went to Plugins -> Installed plugins -> Ecwid shopping cart, and clicked 'Edit'.
I made a minor change to ecwid-shopping-cart.php but found that after the change, the Ecwid stuff didn't load properly on our site; even worse, I was unable to load wp-admin/ (get blank page).
I used FTP to replace ecwid-shopping-cart.php, but this did not fix the problem!
I've deleted and replaced the entire contents of that plugin, but no help.
I deleted everything in wp-content/cache/ but this didn't help.
I renamed the ecwid-shopping-cart plugin folder so that it wouldn't load at all, but no help.