When you're installing a theme on your Nokia N95 cellphone usually you will face two kind of certificate error. Here is the guide to fix those problems:
Certificate Error:
Go to "App. Mgr."
press "Options"
press "Settings"
make sure "Software installation" is set to "All" and "Online certif. check" is set to "Off".
Expired Certificate:
If you encounter Expired Certificate error during installation on to your Nokia phone, please set your mobile phone date back 1 year before you install your theme. Set the date back after installation.
Hope it helps!
Tips source
Certificate Error:
Go to "App. Mgr."
press "Options"
press "Settings"
make sure "Software installation" is set to "All" and "Online certif. check" is set to "Off".
Expired Certificate:
If you encounter Expired Certificate error during installation on to your Nokia phone, please set your mobile phone date back 1 year before you install your theme. Set the date back after installation.
Hope it helps!
Tips source