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Are you seeing an error number? The steps in this article may helpful even if you don't have this specific error number:
Adjust your certificate settings:
Mac OS X:
From the Finder, in the Go menu, choose Utilities.
Open Keychain Access.
From the Keychain Access menu, choose Preferences.
Click on the Certificates tab.
Choose Off under Online Certificate Status Protocol (OCSP)
Choose Off under Certificate Revocation List (CRL).
Restart your Mac.