Debian Certificate Error (no replies)

Dear Friends,

Whenever i setup everything and try to download in Debian i am getting this error

ERROR: The certificate of ' domain name' is not trusted.
ERROR: The certificate of ' domain name' doesn't have a known issuer.

Till these days i was downloading from a different server and tried to copy to my debian Box.

Today, i thought let me ask the community for a solution.

Does https not supported on Debian 5.2.9 ?

I am running 5.2.9 on a PogoPlug V4.