Magento

The installation didn’t work: 

Checking dependencies of packages

CONNECT ERROR: Package ‘Magento_Mobile’ is invalid
‘./skin/adminhtml/default/default/images/xmlconnect/design_default/accordion_open.png’ already exists
Package ‘Mage_Core_Modules’ is invalid
‘./app/code/core/Mage/Admin/Model/Acl/Assert/Ip.php’ already exists
Package ‘Lib_Varien’ is invalid
‘./lib/Varien/Autoload.php’ already exists
Package ‘Lib_Google_Checkout’ is invalid
‘./lib/googlecheckout/googlecart.php’ already exists
Package ‘Lib_Js_Calendar’ is invalid
‘./js/calendar/calendar-blue.css’ already exists
Package ‘Lib_Js_Mage’ is invalid
‘./js/lib/FABridge.js’ already exists
Package ‘Lib_Phpseclib’ is invalid
‘./lib/phpseclib/Crypt/AES.php’ already exists
Package ‘Mage_Locale_en_US’ is invalid
‘./app/locale/en_US/Mage_AdminNotification.csv’ already exists
Package ‘Lib_Mage’ is invalid
‘./lib/Mage/Archive/Abstract.php’ already exists
Package ‘Lib_ZF’ is invalid
‘./lib/Zend/Acl/Assert/Interface.php’ already exists
Package ‘Lib_Js_Prototype’ is invalid
‘./js/prototype/debug.js’ already exists
Package ‘Lib_ZF_Locale’ is invalid
‘./lib/Zend/Locale/Data/Translation.php’ already exists

Please check the output frame for errors and refresh the page to retry changes.

using version 1.5

Try to use correct extension key for your version of magento.
see table here:
http://www.magentocommerce.com/magento-connect/Magento+Core/extension/4457/magento_mobile

key for v.1.5.0.1:  http://connect20.magentocommerce.com/community/Magento_Mobile-1.5.0.0.19

P.S. for v1.5.1.0 you don’t need to install extension, you already have it installed (newer version doesn’t exist at the moment)