If you were locked out of the admin panel with an error after you've installed the new version through the Magento Connect, most probably, you have a Compilation option enabled in your Magento.
Before to start the installation process via Magento Connect, it's vital to:
- disable Compilation option in your Magento if it is enabled;
- make sure you have full write permissions to all Magento files and folders;
- make your server configurations comply with the next requirements:
- Max execution time = 360 seconds or more,
- Memory limit = at least 512 MB.
To solve the issue you've faced, please disable a Compilation option before installation and enable the cache in Magento. Once an Extension is installed, you should run the Compilation option again.
In case you cannot access Magento admin panel, disable a Compilation option in the next way:
- Go to the Magento installation folder and open file includes/config.php.
- Comment out the two define function calls and save this file: