Recently there have been a common issue when setting up Lync Server 2013's Persistent Chat.
This issue has become so common that Microsoft's has started a Lync Forum titled 'Lync Server 2013 - Persistent Chat'

First, What is Lync Persistent Chat?
Microsoft has changed the name from Group Chat which existed in Lync 2010 to Persistent Chat in Lync 2013. When an end user leaves messages in a chat room, the IMs stay in the specific chat room's session for others to see and respond to. The fact than an IM session isn't removed when an end user ends the session is why it's known as persistent.

Second, what is this issue?
After going through the steps to configure the Persistent Chat on Lync 2013, when you go to the Lync Server 2013 Control Panel you will see 'All Channel Servers are down".

How to fix this?
The very fact that you are reading this article means that you have experiencing these warning and error messages. Hence it is in your best interest to go back to your Topology Builder and delete the Chat Pool and rebuild it.

First delete the chat pool you created in the Lync Server 2013, Topology Builder.
Second, go to your Lync Server 2013 - Deployment Wizard, click on Install on Update Server System and run Step 2: Setup or remove Lync Server Components again.

You can follow the steps described by Matt Landis in his great article about 'Step by Step Installing Server 2013 Persistent Chat Collocated on Standard Edition Front End', however, there are a few exceptions.

Below are these changes-

1. Hopefully you have created a SA account to install and configure Lync. Tentatively give that SA account Enterprise or Domain Admin rights.
2. Make that SA account a Local Admin in both the Lync Front End (FE) and the SQL server that you are using.
3. When you are setting up the New Persistent Chat Pool in the Topology Builder, Matt Landis suggests to create a new SQL Instance. DO NOT DO THAT. Check the 'Default Instance' radio button.

 Make sure that you do not encounter any errors when you are publishing the topology.

I would like to point out that this article isn't intended to bash Matt Landis in anyway. If it wasn't for his detailed articles I wouldn't have learnt so much about Lync 2013 setup and configuration.
Matt Landis, I salute you!!

You are welcome to visit my other blogs which are listed below.

1. SharePoint 2013: Create InfoPath forms using existing Excel Forms.
2. SharePoint 2013: Setup Document Library Permissions.