Question

Possible Duplicate:
Magento error: Module “Mage_Api” requires module “Mage_Core”

error list when I open site:

Module "Mage_Api" requires module "Mage_Core".

Trace:
#0 /home/towelsjt/public_html/app/code/core/Mage/Core/Model/Config.php(849): Mage::throwException('Module "Mage_Ap...')
#1 /home/towelsjt/public_html/app/code/core/Mage/Core/Model/Config.php(812): Mage_Core_Model_Config->_sortModuleDepends(Array)
#2 /home/towelsjt/public_html/app/code/core/Mage/Core/Model/Config.php(315): Mage_Core_Model_Config->_loadDeclaredModules()
#3 /home/towelsjt/public_html/app/code/core/Mage/Core/Model/App.php(414): Mage_Core_Model_Config->loadModules()
#4 /home/towelsjt/public_html/app/code/core/Mage/Core/Model/App.php(343): Mage_Core_Model_App->_initModules()
#5 /home/towelsjt/public_html/app/Mage.php(683): Mage_Core_Model_App->run(Array)
#6 /home/towelsjt/public_html/index.php(87): Mage::run('', 'store')
#7 {main}

Answer 1

This error message is letting you know that Magento tried to load the Mage_Api module’s declaration, but couldn’t find a declaration for the Mage_Core module. Since Mage_Api is configured to depend on this module, Magento bails.

There’s myriad reasons this could happen, and there’s not enough information in your question to deduce what’s going on. You’ll need to debug this problem further yourself.

First, this exception is emanating from the following method

#File: app/code/core/Mage/Core/Model/Config.php
protected function _sortModuleDepends($modules)
{
    ...
}    

The $modules array contains the loaded app/etc/modules information for your system. Your exception comes up in the first loop

foreach ($modules as $moduleName => $moduleProps) {
    $depends = $moduleProps['depends'];
    foreach ($moduleProps['depends'] as $depend => $true) {
        if ($moduleProps['active'] && ((!isset($modules[$depend])) || empty($modules[$depend]['active']))) {
            Mage::throwException(
                Mage::helper('core')->__('Module "%1$s" requires module "%2$s".', $moduleName, $depend)
            );
        }
        $depends = array_merge($depends, $modules[$depend]['depends']);
    }
    $modules[$moduleName]['depends'] = $depends;
}

Check the contents of $modules. If there’s not a Mage_Core key (as I suspect), that means Magento couldn’t load the file in app/etc/modules that declares Mage_Core. By default this is Mage_All.xml. Check permissions on this file, and check that it’s valid XML. If cursory checks pass, this file is loaded in _loadDeclaredModules

protected function _loadDeclaredModules($mergeConfig = null)
{
    //...
    foreach ($moduleFiles as $file) {
        $fileConfig->loadFile($file);
        $unsortedConfig->extend($fileConfig);
    }    
    $moduleDepends = array();
    foreach ($unsortedConfig->getNode('modules')->children() as $moduleName => $moduleNode) {
        if (!$this->_isAllowedModule($moduleName)) {
            continue;
        }

        $depends = array();
        if ($moduleNode->depends) {
            foreach ($moduleNode->depends->children() as $depend) {
                $depends[$depend->getName()] = true;
            }
        }
        $moduleDepends[$moduleName] = array(
            'module'    => $moduleName,
            'depends'   => $depends,
            'active'    => ('true' === (string)$moduleNode->active ? true : false),
        );
    }

    //...
}

Determine why the Mage_Core node is missing, and you’ll find the solution to your problem.