I thought that this would be fixed from the BETA but it looks like it is not at this point. I am trying to import a UC certificate from Go Daddy via the GUI and get an error of "The souce data is corrupted or not properly Base64 encoded". This is a known BETA issue and you must rip the Start Certificate and End Certificate text, save and import. When you do that you are successful and the cert is in the store (you can check it with the MMC plugin for Certificates) but the certificate never shows up in Exchange under Exchange Certificates. Has anyone been able to successfully import a third party cert from the GUI in 2010 RC? Love to know..