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"Content was blocked" message


The web part on my landing page is displaying the message "Content was blocked beause it was not signed by a valid security certificate." It was working fine Friday afternoon, and then this was noticed first thing Monday morning. The only change we can think of is a Java update late last week. We're now on update 141. The message is showing in Internet Explorer and Firefox. Here is the Firefox error message: uses an invalid security certificate.
The certificate is not trusted because the issuer certificate is unknown.
The server might not be sending the appropriate intermediate certificates.
An additional root certificate may need to be imported.
The certificate expired on July 30, 2017 at 9:05 AM. The current time is July 31, 2017 at 9:54 AM.

What are the steps to fix this?

Thank you in advance.