Cannot get into admin after installation/upgrade via Magento Connect Manager

Q: I installed the new version through the Magento Connect, and it installed fine but then I was locked out of the admin panel with an error. I could only get back in when I uninstalled. Can you help me get this new package installed?

A: Most probably, you have compilation enabled in your Magento, please disable compilation before installation and enable cache in Magento. Once an Extension is installed, you should run compilation process again.

In case you cannot access Magento admin panel, disable it in a next way:

Go to Magento installation folder and open file includes/config.php. Comment out the two define function calls and save this file:

define('COMPILER_INCLUDE_PATH', dirname(__FILE__).DIRECTORY_SEPARATOR.'src');
define('COMPILER_COLLECT_PATH', dirname(__FILE__).DIRECTORY_SEPARATOR.'stat').