Hi,
What application are you trying to install? Is it a cracked application? If it is a cracked application, then you need to get the application signed for your handset's IMEI no. Only then you would be able to install the application.
If you are getting "Expired Certificate" error, then try changing the date to past (e.g., 1/2/2008) & try installing.
"If this post helped you resolve your query, please do click the KUDOS tab."
Message Edited by sujaythelibran on 09-Dec-2009 01:24 PM