how do i get my new purchased exchange comercial certificate to work on my laptop outlook

I've had my exchange server 2003 up and running since october of 2008, initially I had a bunch of issues setting up outlook to work outside the local network.  Finally I figured out that the certificate needed to be installed in the trusted Root directory of any laptop outside the network.  It's been working fine but lately I started having issues with certificates disapearing from the root directory, and constatly had to upload them back into the trusted root directory.  Finally after reading some of the other posts you have on your website, I realized that Comercial certificate is the way to go.  I went to the rapid ssl website and grabed a 30 day free certificate to test if it worked better for us.  I got it uploaded into the Default Website and replaced the old certificate.  The only problem I'm having now is I can't figure out the settings on my laptop to work with this certificate or if I missed something during the installation of the new certificate.  When I test the certificate on the Rapid SSL support page, it gives me the following

ERROR MESSAGE: Error: The certificate installation checker connected to the Web server and read its certificates, but could not determine which is the primary certificate for the Web server. Make sure that the domain name entered above matches the common name of the certificate installed on the Web server.  

Can Someone please help
Thanks
Rick