Error when applying "Update" order status

Hello,

When I choose the order status "update" and submit it via the order management panel, I receive a white page. The debug file in cache says this:

[05-Apr-2012 11:00:52] PHP Fatal error: Call to undefined function date_diff() in /home/mydirectory/public_html/myadmin/orders.php on line 148

In reference to this line in the orders.php file:

$zc_max_days = date_diff($check_status->fields['date_purchased'], date('Y-m-d H:i:s', time())) + DOWNLOAD_MAX_DAYS;

Any ideas on how I can fix that issue?

Thanks!

hockey2112:

In reference to this line in the orders.php file:

$zc_max_days = date_diff($check_status->fields['date_purchased'], date('Y-m-d H:i:s', time())) + DOWNLOAD_MAX_DAYS;

> 
> Thanks!

This is code from zencart v1.3.8.  You need to update ASAP. 

Cheers
Rod

It must have "snuck in" with an old module installed a year or so ago. Thanks for your help!