error activating full license

[cnations]

I purchased a full license 2 days ago, but since then I have been unable to activate the license. Whenever I try, I get the following error: "Unable to connect to license server: javax.net.ssl.SSLHandshakeException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target". Is this a problem with the license server, or something on my end? Currently, I have a starter license running.