Invalid Security Certificate

I had a problem last week with my computer. I cannot open more windows but can only open one. Everytime I opened yahoo.com, it says the following message below;

"us.data.toolbar.yahoo.com443 invalid security certificate .how can i fixed this? thank you.
I had the same problem and resetting the time and date in control panel solved it - for some reason the time had been set back to a date in 2005. I resync'd using the "windows sync" optin and all's well again"

I noticed that the time and date of my computer is not updated. I don't know what's wrong but since I updated my firefox browser to 3.6 version last week this weird thing already happened. I tried to change the right date and time of my pc and bingo! I can already open another browser and the message above stopped popping-up already. My pc is back to normal again!