Magento Connect “Exception during cache and session cleaning” Error

When using the Magento Connect manager with certain browsers you may receive an “Exception during cache and session cleaning” error message in the Magento Connect output frame when attempting to either install or reinstall LiteMage. If this occurs, LiteMage will still be installed but your Magento site will become stuck in maintenance mode and therefore be inaccessible.

The reason for this is that when Magento Connect attempts to install any new modules to your store, it first creates a “maintenance.flag” file in the root directory. The presence of this file signals that your site is now in maintenance mode and changes can be safely made. Under normal circumstances this file should be automatically deleted once the installation has completed, but certain errors (such as this one) can cause Magento Connect to halt before reaching the removal step.

To fix this simply delete the “maintenance.flag” file from the root folder of your affected Magento site.