If you’re struggling to install an extension from the Magento Connect Manager, review the var directory permissions.

The quickest approach appears to be this series of steps:

  1. Delete the files from within var/cache and var/session
  2. Temporarily reset the permissions of var directory and files recursively to 777.
  3. Attempt extension install in the Magento Connect Manager
  4. The install should have worked. Now the permissions of the var directory need to be corrected:
    1. Set the directory permissions to 755 recursively
    2. Set the file permissions to 644 recursively

Two issues may have risen during the failed install:

  1. The site is stuck in maintenance mode – find the maintenance.flag file in the root and delete it
  2. The site has hit an error but will not display it – Navigate to the “errors” folder, change local.xml.sample to local.xml. This will list the error details for you to then resolve.