UPSXML error: Rating and Service 1.0001 0 unknown

Hi everyone!

I have done some extensive searching, this forum and related support forums (including other ecommerce platforms) and I have not been able to solve this issue.

On check out we are getting the following (regarding UPS xml plugin):

"Rating and Service 1.0001 0 An unknown error occured while attempting to contact the UPS gateway : Rating and Service 1.0001 0 An unknown error occured while attempting to contact the UPS gateway"

I have uncommented the following line (as suggested across both zendesk, oscommerce and other forums) in the ups xml file:
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);

The error still occurs.

Here is some information regarding our installation:

Zen Cart 1.3.8a
Database Patch Level: 1.3.8
PHP Version 5.2.17
Linux 3.12.41-77.ELK6.x86_64

thank you in advance for any tips or suggestions.

Actually, I'm surprised that anything is working or that you haven't become victim to a version so old that none of the mods can be expected to work or support it.
Nine years is a LONG time in the software world. PHP is now to version 7.0 Linux Kernel is at 3.15.5 Zen Cart is now 1.5.5a and a LOT different than the 2007 model.
I am shocked that your host is running software so old.
Unfortunately, you have little options beyond upgrade and I'm not sure that any of the newer shipping mods will work with that version of PHP. Zen Cart 1.5.5a will run for upgrade BUT, you would need to upgrade the server before adding mods as they may not work with 5.2.17.
Sorry I don't have a better solution for you.

The message suggests that CURL is failing.

The module appears to have some built-in logging capability if you enable it in the PHP file. At line 91 you'll see instructions, and then need to uncomment (remove the // from the beginning of) line 92:

91:        // to enable logging, create an empty "upsxml.log" file at the location you set below, give it write permissions (777) and uncomment the next line
92:        // $this->logfile = DIR_FS_CATALOG . 'includes/modules/shipping/upsxml.log';

Then you can see what errors are occurring by viewing that log file after triggering the error.

I recommend also installing this plugin to help diagnose other PHP errors which are likely rampant on your site due to PHP compatibility issues from using old software on newer PHP versions: https://www.zen-cart.com/downloads.php?do=file&id=606