Hi.
Import the correct Certificate and Install it in IIS

You can follow below mentioned blogs for your reference
http://blogs.technet.com/b/sbs/archive/2008/09/20/introducing-the-add-a-trusted-certificate-wizard-in-sbs-2008.aspx
Introducing the “Add a Trusted Certificate Wizard” in SBS 2008

http://blogs.technet.com/b/sbs/archive/2009/12/14/how-to-manually-install-certificates-in-sbs-2008.aspx
How to Manually Install Certificates in SBS 2008
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also so check this link
http://support.microsoft.com/kb/2417228