Error message at checkout

Started getting an error message when customers attempt to proceed to check out:

Warning: include_once(includes/modules/order_total/ot_subtotal.php) [function.include-once]: failed to open stream: No such file or directory in /public_html/zen-cart/includes/classes/order_total.php on line 33

Warning: include_once() [function.include]: Failed opening 'includes/modules/order_total/ot_subtotal.php' for inclusion (include_path='.:/usr/lib/php:/usr/local/lib/php') in /public_html/zen-cart/includes/classes/order_total.php on line 33

Fatal error: Class 'ot_subtotal' not found in /public_html/zen-cart/includes/classes/order_total.php on line 36

Can anyone suggest any reasons for this? The files above have not been changed recently.

The ot_subtotal.php file does not exist in the above location - instead it can be found at includes/modules/customtemp/order_total/ot_subtotal.php. Could this be the problem?

I copied the order_total folder (with all files in it, including ot_subtotal.php) into includes/modules just to see what happens and it seems to now allow checkout however the following appears at the top of the checkout page:

DIR_WS_LANGUAGESenglish/modules/order_total/

Any ideas wise people?

Many thanks

The ot_subtotal.php file does not exist in the above location - instead it can be found at includes/modules/customtemp/order_total/ot_subtotal.php. Could this be the problem?
Yes....Did you edit that file?

Only files where you see a classic folder in the tree can be overridden

There is no classic folder at
/includes/modules/order_total/

Thank you for the reply.

No - no files have been edited. The order_total folder just wasn't in includes/modules but was in includes/modules/customtemplate instead (and I'm assuming it must have always been there). This problem only occurred yesterday.

Because I copied the folder from includes/modules/customtemplate into includes/modules it now exists in two locations - is that the reason for the second error message?

I would get a new distribution of the exact same version you are isung and expand it on your local

Compare what and where these files are in the fresh distribution to your files on the server