When changing Order Status in Virtuemart you may see an error vmError: updateStatusForOneOrder unknown virtuemart_order_id which is caused by a small bug in the Virtuemart 4.0.4 package. It will be patched in the next version but in the meantime here's how you fix this Virtuemart Error.
vmError: updateStatusForOneOrder unknown virtuemart_order_id
Before you start, always remember to backup - make sure you have a verified backup of your Joomla Virtuemart software
The problem is caused by a change of variable name in the file '/administrator/components/com_virtuemart/models/orders.php'. Using your favourite FTP program, download this fine and open it in a text editor. Next on line number 1150 replace:
Then you can upload the file to replace the older version and solve the problem.