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This article speaks about a similar issue and might be helpful<br />
<br />
<a href="http://social.technet.microsoft.com/Forums/en-US/ocsclients/thread/ce587d24-7d1e-4779-8606-5932254f54b6" rel="ugc nofollow">http://social.technet.microsoft.com/Forums/en-US/ocsclients/thread/ce587d24-7d1e-4779-8606-5932254f54b6</a><br />
<br />
- Rancy
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This article speaks about a similar issue and might be helpful

http://social.technet.microsoft.com/Forums/en-US/ocsclients/thread/ce587d24-7d1e-4779-8606-5932254f54b6 [http://social.technet.microsoft.com/Forums/en-US/ocsclients/thread/ce587d24-7d1e-4779-8606-5932254f54b6]

- Rancy

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We are in the process of rolling a POC for Lync 2013 Server out. My windows clients connect flawlessly with the 2013 Client.<br />
<br />
When I set Lync up, I did a self signed cert from my DC which up until this point was now when we tried to get a couple of mac clients to connect. <br />
<br />
&quot;Sign in to Microsoft Lync failed because the service is not available or you may not be connected to the internet.&quot; is the error message.<br />
<br />
OSX 10.6.8 and is as up to date as apple will allow it. <br />
<br />
Thoughts?
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We are in the process of rolling a POC for Lync 2013 Server out. My windows clients connect flawlessly with the 2013 Client.

When I set Lync up, I did a self signed cert from my DC which up until this point was now when we tried to get a couple of mac clients to connect. 

"Sign in to Microsoft Lync failed because the service is not available or you may not be connected to the internet." is the error message.

OSX 10.6.8 and is as up to date as apple will allow it. 

Thoughts?

Lync 2011 for Mac - &quot;sign in failed, service not available&quot;

Windows Server 2008 and Windows Server 2008 R2, based on the Microsoft Vista codebase, is the last 32-bit server operating system released by Microsoft. It has a number of versions, including including Foundation, Standard, Enterprise, Datacenter, Web, HPC Server, Itanium and Storage; new features included server core installation and Hyper-V.

Windows Server 2008

Voice over IP (VoIP) is a methodology and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. Other terms commonly associated with VoIP are IP telephony, Internet telephony, broadband telephony, and broadband phone service. The term specifically refers to the provisioning of communications services (voice, fax, SMS, voice-messaging) over the public Internet, rather than via the public switched telephone network (PSTN).  Examples of the VoIP protocols are H.323, Media Gateway Control Protocol (MGCP), Session Initiation Protocol (SIP), H.248 (also known as Media Gateway Control (Megaco)), Real-time Transport Protocol (RTP), Real-time Transport Control Protocol (RTCP), Secure Real-time Transport Protocol (SRTP), Session Description Protocol (SDP), and Inter-Asterisk eXchange (IAX).

Voice Over IP

Instant messaging (IM) is a type of online chat that offers real-time text transmission over the Internet. A LAN messenger operates in a similar way over a local area network. More advanced instant messaging can add file transfer, clickable hyperlinks, Voice over IP, or video chat. Non-IM types of chat include multicast transmission, usually referred to as "chat rooms". Depending on the IM protocol, the technical architecture can be peer-to-peer (direct point-to-point transmission) or client-server (a central server retransmits messages from the sender to the communication device).

Lync 2011 for Mac - &quot;sign in failed, service not available&quot;

Lync 2011 for Mac - "sign in failed, service not available"