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Please click the button marked Show Certificate in the warning dialog. A certificate chain will appear. One or more of the certificates in the chain will be marked with a red X as invalid. Select the uppermost invalid certificate. Some information about it will appear below. Post a screenshot that shows the certificate chain and the problem with the invalid certificate.

That information is not personal, but be careful not to include anything else that is.

Start a reply to this message. Drag the image file into the editing window to upload it. You can also include text in the reply.

Launch the Keychain Access application in any of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad and start typing the name.

In the upper left corner of the window, you should see a list headed Keychains. If not, click the button in the lower left corner that looks like a triangle inside a square.

In the Keychains list, there should be items named System and System Roots. If not, select

File ▹ Add Keychain

from the menu bar and add the following items:

/Library/Keychains/System.keychain

/System/Library/Keychains/SystemRootCertificates.keychain

Open the View menu in the menu bar. If one of the items in the menu is

Show Expired Certificates

select it. Otherwise it will show

Hide Expired Certificates

which is what you want.

From the Category list in the lower left corner of the window, select Certificates. Look carefully at the list of certificates in the right side of the window. If any of them has a blue-and-white plus sign or a red "X" in the icon, double-click it. An inspection window will open. Click the disclosure triangle labeled Trust to disclose the trust settings for the certificate. From the menu labeled

Secure Sockets Layer (SSL)

select

no value specified

Close the inspection window. You'll be prompted for your administrator password to update the settings.

Now open the same inspection window again, and select

When using this certificate: Use System Defaults

Save the change in the same way as before.

Revert all the certificates with non-default trust settings. Never again change any of those settings.