Security alert Verisign certificate

Hi,

we are publishing a Owa/Exchange 2003 site on a Isa 2004. Installed a
Verisign certificate.
However when I enter the Owa site I get a security alert stating that:

The security certificate was issued by a company you have not chosen to trust.

When I view the certificate it says:

This certificate cannot be verified up to a trusted certification authority.

What can this be?