Login to the DCM
Select a Certificate Store (default is *SYSTEM)
Enter password and continue
On the left drop down menu, click on Fast Path
Select Work with CA certificates
This will display all the current CA (Certificate Authority) and their status. You will see entries like VeriSign, RSA, etc. If the one you are using is listed, change the status to ENABLED by clicking on Enable.
If it is not listed, click on Import at the bottom and add the new issuer (Digicert for example)