When trying to login to Plesk if you receive the following error then the steps below should correct the issue:

getProductVersion failed

1. Check the file '/usr/local/psa/version' to see if it is empty:
   
   # cat /usr/local/psa/version
2. If the version file is empty then you will need to run the following command to see what version of Plesk is currently installed:

   # rpm -q psa
   psa-8.0.0-rhel4.build80060425.18
   

3. Now you will need to add the above line to '/usr/local/psa/version':

   vi /usr/local/psa/version
   80060425.18

4. Next restart Plesk and you should be able to login:

   # /etc/init.d/psa restart
   Processing config directory: /usr/local/psa/admin/conf/httpsd.*.include
   Syntax OK
   /usr/local/psa/admin/bin/httpsdctl restart: httpd restarted