I have a system that has been running OCS 2007 R2 for some time now.   Recently one of the arrays on the drive suffered a failure.  I recovered the drive and it's back on line. 

When the system starts up, OCS services are all running. Nothing in the logs shows any issue.  When I go to any client, on any system, I get the message:

Cannot sign in because the server is temporarily unavailable.  If the problem persists, contact your system administrator.

There is nothing on the client system logs.

The server logs show the messages: 

--The WMI event provider could not connect to pool backend server.  Pool backend: '(local)\rtc'.

--Failed processing conference status requests. This error might delay the freeing up of PSTN meeting ids in conference directories ---homed on this pool.

--Error code: 0x800407D0

--Cause: Possible issues with back-end or Office Communications Server health.

--Resolution:

--Ensure the Office Communications Server service is healthy.

I don't see any other controls for Communicator.  Granted it's been a while since install and all, and since it's running no issues I didn't touch it.  Can someone help with what I may be missing here please? 

Try to sign in with OCS client on the same computer with OCS server. You should check the failure didnt cause the loss of data. Check the back end server connectivity is fine.

Using OCS  client on the host server gives the same result.  

Communicator was not originally installed on the drives that had failed. That's the confusing part for me.  

I ran the logs and found a failure report in the section for Check User Logon:

Failed to register user: User sip: ****@******.com @ Server *******.***.com
Failed registration response: [
SIP/2.0 503 Service unavailable
FROM: <sip:*****abraun@connance.com>;epid=epid00;tag=0f2c7f82d
TO: <sip:****@******.com>;tag=45D177886BB3CE2028B7E7B95BDB77A8
CSEQ: 2 REGISTER
CALL-ID: a67584d733ca41399e1e6eebd99909b6
VIA: SIP/2.0/TLS 10.0.0.11:4633;branch=z9hG4bKb616e496;ms-received-port=4633;ms-received-cid=3D700
CONTENT-LENGTH: 0
AUTHENTICATION-INFO: Kerberos rspauth="602306092A864886F71201020201011100FFFFFFFFC92FD0A710ED2E3E940AC484D673C7FB", srand="55A3AD37", snum="1", opaque="0F44B019", qop="auth", targetname="sip/*******.***.com", realm="SIP Communications Service"
RETRY-AFTER: 86
ms-diagnostics: 4144;reason="Database communication link is down";source="connance1.hai.com"
]

Hi

Check if all the Database server are running. Check if you are able to ping the Database server.

Thank you Raju_raju. 

I found the database rtcdyn in (suspect) status.  I've attempted recovery but at the moment it's not usable.  This seems like a good starting point.  Is there a way to rebuild this database?   This stores chat information from what I remember but I imagine there is a lot of pieces in here and I want to get the schema put back in.  I'd like to remake it to see if I can get communicator up with this if possible.  

Please check the event view of the Back End Server. I dont think the problem is only related with the Rtcdyn database as you cant connect the back end server.

Turns out that the Database corruption was the reason that it wouldn't start.  A database restore would fix this.  Thanks to all for your help.