There is something wrong with the installation of your certificate. When correctly installed it will not give any warnings. We will be happy to help you in any way we can.
Have you installed both the root and intermediate certificates? Incomplete installation is most likely the cause of the alert you are receiving.
Have you restarted the server since the certificate was installed?
Please reference our SSL Certificate Installation Instruction. You will need to select your Server Platform in the menu on the left.