problem with signing in

[paha]

Hello,
I can´t sign in almost a week now. If i try to sign in I get his note:

Unable to validate certificate
The certificate for omega.contacts.msn.com could not be validated. The 
certificate chain presented is invalid.

What that means? I already downloaded a newest version, and I still 
can´t sign in. I use Pidgin almost 2 years, and this is a first time, if 
the error occure.

Ene