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

You cannot sign in to Microsoft Office Communicator 2007 R2 or Microsoft Lync 2010 in a dedicated Business Productivity Online Suite environment. Additionally, you receive the following error message:

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

There are multiple causes behind this issue, such as:

§  You are not entitled for Office Communicator Online or Lync Online.

§  You lack connectivity to the OCS or Lync service.

§  You are running a 64-bit Windows operating system.

Note: This cause only applies to Communicator 2007 R2.

I am sharing both the resolutions that I tried by considering multiple scenarios so suggest you to test the both solutions:

Resolution:

1.   Microsoft Managed Services Service Provisioning Provider (MMSSPP) provisions managed account objects for OCS according to your organization's specific logic. Some organizations use an OCS or Lync entitlement flag (such as  extensionattribute5 ) in their Active Directory to signal MMSSPP to provision that object for OCS or Lync. The value of the OCS or Lync entitlement flag is specific to each organization. Other organizations provision all users with a certain Primary SMTP domain.

2.   There is a known issue with Office Communicator 2007 and 64-bit operating systems that prevents Communicator from being able to successfully authenticate. To resolve this issue, update the user’s registry as follows:

§  Start Notepad. 

§  Copy the following text exactly as it is into the notepad file:

§  Windows Registry Editor Version 5.00[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa]"LmCompatibilityLevel"=dword:00000002 

§  Save the notepad file as 64bitfix.reg . 

§  Shut down Office Communicator and verify communicator.exe process is not running from the Task Manager. 

§  Execute the file by double-clicking the 64bitfix.reg file. 

§  Restart the computer and then start Office Communicator again