|Often that's caused by your computer's date being wrong. The security certificates are issued for a specific time period. If the date showing on your computer falls outside that period--either before or after--then you can get that error.|
That error can also be associated with unsigned activex controls. Here's some info on that:
You may need to set google and gmail as trusted sites if your security level in internet options is set high.
Or as already mentioned, it may be a malware problem.