2016-02-12T23:20:54+00:00 ERR (3): Warning: include(Mage/Namespace/Package/Helper/Data.php): failed to open stream: No such file or directory  in /var/www/magento1/lib/Varien/Autoload.php on line 94
2016-02-12T23:20:54+00:00 ERR (3): Warning: include(): Failed opening 'Mage/Namespace/Package/Helper/Data.php' for inclusion (include_path='/var/www/magento1/app/code/local:/var/www/magento1/app/code/community:/var/www/magento1/app/code/core:/var/www/magento1/lib:.:/usr/share/php:/usr/share/pear')  in /var/www/magento1/lib/Varien/Autoload.php on line 94

class Namespace_Package_Helper_Data extends Mage_Core_Helper_Abstract
{
    public function test()
    {
        echo 'Helper loaded';
    }
}

<config>
    <global>
        <helpers>
            <namespace>
                <class>Namespace_Package_Helper</class>
            </namespace>
        </helpers>
    </global>
</config>

$helper = Mage::helper('namespace/data');
$helper->test();

<config>
    <menu>
        <namespace module="namespace_package">
            <title>Namespace</title>
            <sort_order>200</sort_order>
                <children>
                    <overview>
                    <title>Overview</title>
                    <sort_order>1</sort_order>
                    <action>adminhtml/namespace/index</action>
                </overview>
            </children>
        </namespace>
    </menu>
    <acl>
     <resources>
        <admin>
            <children>
                <namespace module="namespace_package">
                    <title>Top Level Namespace Menu Item</title>
                    <sort_order>1</sort_order>
                </namespace>
                </children>
            </admin>
        </resources>
    </acl>
</config>

<config>
    <menu>
        <namespace module="namespace">
            <title>Namespace</title>
            <sort_order>200</sort_order>
                <children>
                    <overview>
                    <title>Overview</title>
                    <sort_order>1</sort_order>
                    <action>adminhtml/namespace/index</action>
                </overview>
            </children>
        </namespace>
    </menu>
    <acl>
     <resources>
        <admin>
            <children>
                <namespace module="namespace">
                    <title>Top Level Namespace Menu Item</title>
                    <sort_order>1</sort_order>
                </namespace>
                </children>
            </admin>
        </resources>
    </acl>
</config>