If you're getting the 'invalid security certificate' error message when trying to log into Facebook, there could be several things wrong with your computer.
Incorrect time and date setting on Windows
If your I.P. is from a certain time zone, but your Windows date and time settings are 'off' or different, some sites will see this as a possible threat. Make sure your Windows date and time settings are correct.
Sync Windows clock with internet time server
- Right mouse click on the time displayed in the lower right side of your Windows task bar.
- Select the 'Adjust time/date' option.
- Click the 'Internet Time' tab.
- Make sure it says ~ "This computer is set to automatically synchronize with 'time.windows.com'". Adjust the settings as necessary and save your changes.
You browser's cache is outdated
Make sure your browser's cache is current by clearing it, then navigate back to Facebook and attempt to login again.