Problem
Users will sometimes encounter an error when trying to access a secure (SSL or HTTPS) website. Error messages may indicate either an "invalid certificate" or an "unknown certificate error" when trying to make an SSL secure connection.
Environment
Internet Browser
Resolution
Some FTP clients such as Filezilla and certain e-mail clients will display an error message when encountering an unknown security (SSL) certificate.
It is generally safe to "click through" the error by clicking OK.
To avoid a repetition of the error, click the checkbox to Always trust before clicking OK.
Cause
A previously known security (SSL) certificate will sometimes become unknown when renewed or updated to a new expiration date.