What to do if the Client browser gives an error while accessing Servers with Intranet SSL?

Check this:

1. Please check if you have installed Intranet Root/Intermediate CA Certificates on Windows PCs or Macs. If they are already installed then it could be an antivirus blocking access to the root certificate, thinking that is not a trusted root certificate. In this case, create an exception in the setting of the anti-virus to allow access to SecureNT Intranet root/intermediate CA certificates.
2. On Windows PCs ensure that Intranet Root CA Certificate is installed under “Trusted Root Certification Authorities”; and that Intranet Intermediate CA Certificate is installed under “Intermediate Certification Authorities”.

To install the SecureNT Intranet Root/Intermediate CA Certificates follow the steps given here. They need to be installed once, on each Windows client PC. On a Mac, customers will need to open Keychain Manager and explicitly trust each of the two root certificates.

To automate the installation of root certificates on multiple machines, one can use Microsoft’s Group Policy for PCs; and Parallel’s Device Management for Macs. Click here to find the installation details. (https://intranetssl.net/support/resources/)

Firefox does not use the operating system’s certificate store for storing the root certificates. So, the root certificate chain is added differently. Read this article for details. (https://support.mozilla.org/en-US/kb/setting-certificate-authorities-firefox)