gmail untrusted certificate!

I’m from Iran and I tried to connect to my gtalk account using Pidgin
but it says Gmail certification is not trusted.
i’ve got a screenshot show the datails, what do you think?

http://imageupload.co.uk/files/ud6i0psm2rjskqbv6p56.jpg

Hi

My parents had a similar issue, turned out the date/time on their PC had changed and was set to before the certificate was valid from date/time.

Garry

Thanks
But date and time is set.