What is likely causing the connection issue?

You are the Microsoft Lync Online administrator for your company. A customer has reported an
issue when signing in to the company’s Lync Online Service. When the customer attempts to sign in,
the following error message is returned:
“The server is temporarily unavailable”.
The server is up, and other customers are connected to it.
What is likely causing the connection issue?

A.
The user has the incorrect Lync version

B.
The user has entered the wrong user name

C.
DNS is configured incorrectly

D.
The user does not have a Lync license

Explanation:
This issue occurs for one of the following reasons:

Cause 1: You are not entitled for Lync Online.
Cause 2: You lack connectivity to the Lync Online service.
Cause 3: You are running a 64-bit Windows operating system.
“Cannot sign in because the server is temporarily unavailable” error when you try to sign
in to Lync Online in Office 365 dedicated
https://support.microsoft.com/en-us/kb/2619522