If you installed Microsoft Office 2013, your Lync client will be upgraded to the 2013 version. If you are in an Office Communication Server 2007 (OCS 2007) environment, this can cause an incompatibility issue. You’ll get an error when you attempt to sign in that says “Cannot sign in because the server version is incompatible with Microsoft Lync. Contact your support team with this information.” Fortunately, there is a registry hack that will get you working again.
1. Select Start, type regedit, then press Enter.
2. Navigate to the following path:
3. Create a new DWORD 32-bit value called DisableServerCheck and set the Data to 1.
Now close out of the Registry Editor and give it a try. Lync 2013 should work just fine now with OCS 2007.