For Mac OS clients, you should have been given a certificate to install on your computer. Depending on the setup of the Citrix system, there may even be more than one certificate to install.
If you get the error when you first log into the Citrix web login, then the first problem is that you need to tell your computer's web browsers to trust the certificate, meaning it probably needs to be added to your system keychain. To do this, you double-click the certificate file which should open up the keychain manager. Select the System keychain from the dropdown and hit OK.
If you get the error after clicking on an application after logging in, then you need to tell Citrix to trust the certificate which is what the instructions I put in my last post are for. I wish I could tell you if any of the certificates in your cacerts folder were the right one, but unfortunately, the name of the file doesn't really mean anything.
If you do not have this certificate(s), you should contact your company's support people and tell them that you need the SSL certificate or certificates used for the Citrix Web Interface and Citrix Secure Gateway.