The latest version of ArubaOS comes with a self-signed certificate that is not trusted by anyone. You can make the error go away by uploading an SSL certificate to the controller that is (1) Trusted by your client and (2) whose hostname resolves to the URL of the controller. You can either do this by (1) generating and uploading your own self-signed SSL certificate that is trusted by your clients or (2) Obtaining an SSL certificate from a public certificate authority that is trusted by your clients.
The controller will give you certificate errors on the GUI if:
- The certificate is expired
- The certificate is revoked
- Your client does not trust the CA that issued the certificate
- the common name of the certificate on the controller does not match the URL you typed to access the controller
That is the simplest explanation. Please look for a detailed explanation and how to fix it here: https://community.arubanetworks.com/t5/Controller-Based-WLANs/ArubaOS-Default-Certificate-Revocation-FAQ-Controllers/ta-p/275809