Schannel 36882

I am using a SQL Server 2005 SP2 on a newly installed Windows Server 2003 with SP2 and AD member server. I am getting the following message in Event Log:

Source: Schannel
ID: 36882
The certificate received from the remote server was issued by an untrusted certificate authority. Because of this, none of the data contained in the certificate can be validated. The SSL connection request has failed. The attached data contains the server certificate.

Can anyone explain me what is this error and how to solve it? Thanks.