shopping_cart.php error when changing quantity

[lismith]

I searched and didn't find anything about this problem. I'm getting this error when quantity is changed in the shopping cart:

Warning: Illegal offset type in (path)/includes/classes/shopping_cart.php on line 495

Warning: Cannot modify header information - headers already sent by (output started at (path)/includes/classes/shopping_cart.php:495) in (path)/includes/functions/functions_general.php on line 44

I haven't made any modifications to either of these files, and I reuploaded them thinking they may have been corrupted.

Where else could this error be coming from? I don't have a clue where to look.

Line 495 in shopping_cart.php is the 3rd line in this block of code:

  function get_quantity($products_id) {
    $this->notify('NOTIFIER_CART_GET_QUANTITY_START');
    if (isset($this->contents[$products_id])) {
    $this->notify('NOTIFIER_CART_GET_QUANTITY_END_QTY');
      return $this->contents[$products_id]['qty'];
    } else {
    $this->notify('NOTIFIER_CART_GET_QUANTITY_END_FALSE');
      return 0;
    }
  }

and line 44 of functions_general.php is:

    header('Location: ' . $url);

HELP!?

[DrByte]

What customizations have you made to your site?
What addons/contributions have you installed?
What version of Zen Cart are you using? What patches have you applied? Was this an upgrade from a prior version? Which version?
Can you share a URL where this can be seen in action?
When did it start happening?
Does it happen with all products, or just certain ones?

[lismith]

It's version 1.3.7, full install not upgraded from any previous version. I installed the "Additional Product Fields" mod by TheOracle. It never worked correctly -- in fact, it was a problem with shopping_cart.php -- so I've removed all files added by the mod and restored the other files that had been modified. I actually didn't notice the problem until today so it may have been there before I uninstalled the mod. I've went thru the install for that mod twice, trying to find if I've missed something. I probably have, but don't have any idea where to start looking. I've made a lot of changes to the template but I don't think any of them would cause this problem.

The site is www.bamagolfcart.com

[lismith]

I also added a new field using the instructions posted by crazy_chris at http://www.zen-cart.com/forum/showthread.php?t=57924, but it's not being used in the shopping cart so I didn't think it would cause a problem.

[DrByte]

As a start, i suggest that you backup your existing files:
/includes/classes/shopping_cart.php
/includes/main_cart_actions.php

and replace those from a fresh v1.3.7 zip.

It's always a good idea to do a complete file+database backup periodically while making customizations.

[lismith]

Thanks for the advice Dr. Byte. I restored the original files you mentioned and still have the error. Is there anything in the mysql database that would cause this problem? I'd thought it probably had to do with the additional product fields mod or adding the new field with crazy_chris' instructions but I've went through everything and haven't seen any problem (although it's entirely possible I've missed something.) Just wondering if there might be other possible reasons for it.