Problem deleting orders in Admin

[nemail]

When I try to delete orders in admin, I get the following error:

Fatal error: Call to undefined function: ****include_once() in .../www.xxxxxxxx.com/public_html/catalog/admin/includes/functions/general.php on line 1019

And line 1019 of general.php reads as follows:

****include_once(DIR_FS_CATALOG_MODULES . 'payment/paypal/functions/general.func.php');

I have v2.9 of the PayPal contrib installed and this line is part of that modification.

At the moment, I don't know enough about PHP to troubleshoot effectively. I haven't yet come across a similar problem/solution on this or the osC forums and I don't want to screw anything up, because so far it seems to work perfectly in every other way.

As a quick fix to delete an order, I just swapped in the original general.php file and it worked OK.
But as a permanent solution, I'd like to be able to fix the 'undefined function' error.
Any idea how and where to define it?

Thanks very much for any suggestions.