Nokia 5800 XpressMusic User Manual page 107

Q: Why do I get the error message Expired
certificate or Certificate not valid yet when I am
installing a downloaded application?
A: If Expired certificate or Certificate not valid yet is
displayed, even if the certificate should be valid, check that
the current date and time in your device are correct. You may
have skipped the setting of date and time when starting the
device for the first time, or the mobile network may have
failed to update these settings to your device. To resolve this,
select Menu Settings and Phone Phone mgmt.
> > >
Factory settings. Restore the factory settings, and when the
device restarts, set the correct date and time.
106 © 2009 Nokia. All rights reserved.