Lync Clients suddenly stopped signing in without errors

I have a Lync Server 2013 running with 2013/2010 clients.

As of this morning the clients will no longer sign in.

It just remains in a state saying "Contacting Server and Signing in"

The errors in the error all seem to say something about a an expired certificate but I have no clue what to look for or what to do.

Any help would be appreciated.
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MacleanSystem EngineerCommented:
I was going to outline the steps, but it might be easier following a full instruction set with pictures and all.
You need to use the Certificate Wizard in Lync 2013 as per below.

You just need to establish whether your cert is from an external authority or not if you do not have an internal CA

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vvajjhalaAuthor Commented: are awesome!!

It worked and all clients are up and running.

Thanks so much!!
MacleanSystem EngineerCommented:
Not a problem, happy to have been able to help out. Good luck.
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