Error when editing an order


I have the latest version 2.22, but get the following error when I edit an order :

Warning: Invalid argument supplied for foreach() in /var/www/vhosts/ on line 4755

Any changes I make whilst going through the edit order process are not saved. I have made a few modifications to my site, but can’t imagine that it would have caused this problem. Does anyone have any ideas why this is happening?