SHA-1 Certificates will be rejected by the latest browsers.
Websites and systems protected using certificates using Sha-1 algorithms will no nonger be accepted by new browsers. IE11 and Chrome for example wont allow a user to continue on to the site regardless. Most public CA's have been issuing more scure certificates for some time now, however many internal CA's are still using Sha-1 to sign their certificates. Its time to check and upgrade/reconfigure if you want your systems to keep running smoothly. Microsoft for example has several articles on how to deal with the situation in their support site. I recently helped a customer running Windows Server 2008 Domain to upgrade their CA to issue the higher security certs.