untrusted server cert chain with a trusted certificate issued by Verisign

Hi everyone,

Ive been struggling to fix an issue we have were we are trying to make a connection to a website that has a certificate issued by Verisign.
Ive already read lots of forums which say the same that the error I have is because my certificate is untrusted and I should add it to my cert store, which I already did.

My question is what could be other possible reasons for this exception to be thrown when im using a trusted certificate and the certificate is already in the cert store.

Note: We can make connections to other websites using certificates trusted by Verisign so im trying to figure out what could be wrong with the certificate or with the server we are making the connection with

Thanks!