<ul><li><strong>ROOT CAUSE:</strong> <code>WebmailModel::getRackSpaceAPI()</code> called <code>define("RACKSPACE_EMAIL_ID",...)</code> and <code>define("RACKSPACE_EMAIL_KEY",...)</code> without <code>if (!defined())</code> guards. When <code>ShoppingCartModel</code> was instantiated (via <code>inc_products_manager.php</code> include chain), it created a second <code>WebmailModel</code> instance, triggering duplicate constant warnings on lines 28-29 of <code>Webmail.class.php</code>.</li><li><strong>IMPACT:</strong> PHP warnings were prepended to the <code>getAllProducts</code> AJAX response, causing <code>JSON.parse(res)</code> in <code>displayProductList()</code> to throw <code>Uncaught SyntaxError: Unexpected token &lt;</code> — product list never loaded.</li><li><strong>FIX:</strong> Wrapped both <code>define()</code> calls in <code>Webmail.class.php</code> lines 28-29 with <code>if (!defined())</code> guards. Response now starts with <code>[</code> and passes <code>JSON.parse()</code> cleanly.</li><li><strong>VERIFIED:</strong> Curl test of <code>/controller/product/ProductController.php</code> with action=getAllProducts returns valid JSON <code>[]</code> with no warning prefix.</li><li><strong>Backup:</strong> <code>Webmail.class-bk-v1.php</code> created before modification.</li></ul>