Just had this bite me at one of my customers. Situation: Exchange Server 2007 on Windows Server 2003 R2, upgrading to Exchange Server 2013 on Windows Server 2012. We ordered a new SAN certificate from GoDaddy (requesting it from Exchange 2013) and installed it on the Exchange 2013 servers with no problems. When we installed it on the Exchange 2007 servers, however, the certificates would import but the new certificates (and its chain) all showed the dreaded red X.
Looking at the certificate, we saw the following error message:
If you look more closely at the certificates in GoDaddy’s G2 root chain, you’ll see it’s signed both in SHA1 and SHA2-256. And the latter is the problem for Windows Server 2003 – it has an older cryptography library that doesn’t handle the newer cypher algorithms.
The solution: Install KB968730 on your Windows Server 2003 machines, reboot, and re-check your certificate. Now you should see the “This certificate is OK” message we all love.