Urgent help required, Fatal Error history.php on line 23

[stopshop]

Hi

I have an error that appears when a client clicks on "History & Details of your Orders".

The following error appears in a blank/white page:
Fatal error: Call to undefined method Order::isVirtual() in /home/perfectc/public_html/shop/history.php on line 23

I have replaced this file via ftp a couple of times, but the error persists.
We even confirmed that the file was ok by comparing it (history.php) to another one on another PS store that we have.
Everything seems to be fine with history.php


Can someone please give me an idea of what the problem may be?


Thanks in advance