Certificate Error: This site is not secure, Your PC doesn’t trust this website’s security certificate.

Certificate Error:  This site is not secure, Your PC doesn’t trust this website’s security certificate. 
Error Code: DLG_FLAGS_INVALID_CA

When we browse some website we get this error. The phrase "This site is not secure" is frightening. But trust me there is nothing a user can do about this situation. You literally have  two choices:
1. If you trust the site then click on the  “Go onto the Web page”, it'll take you there. Obviously You can Check the certificate validity. 
Click On Certificate Error --> View Certificate . It'll Popup Certificate details in the right hand site. 

2. You can avoid Entering the website if you do not trust the certificate.

For the administrator you can check the following:
1. Check if the certificate is Installed Properly.
2. Check the Certificate is valid. Check the Certificate validity by Following command in Linux. 
openssl x509 -in certificate.pem -text -noout
3. Check if the Certificate has been Comprised.
4. Clear the browser Cache and try accessing the Certificate  again.
5. If the Certificate is Locally used and Certificate Authority is internal then Most of the browser would not validate it.