Error message "Mage registry key already exists" after extension installation
Mage registry key <...> already exists
The solution is in most cases very easy:
Please confirm that you followed all installation steps that are mentioned in the
README file of the module. Especially assure that the Magento cache is cleared, e.g. by emptying the
var/cache/ directory in a Magento default installation and that the Magento compilation process has been triggered (if enabled).