You’re repeatedly prompted for Exchange credentials after you sign in to Lync

Issue

After you successfully sign in to Skype for Business Online (formerly Lync Online) by using Lync 2010 or Lync 2013, you may experience the following issues:

You receive a message in Lync that says it cannot connect to Exchange.

You're repeatedly prompted to provide a user name and a password to connect to Exchange. You may also receive the following message: 

Credentials are required

 

Note The message that you receive may vary, depending on which service Lync is trying to connect to. You may be prompted for credentials when Lync tries to connect to any of the following services:

Calendar and Free/Busy information from Outlook

Exchange Web Services (EWS)

Response Group Service

Address Book Service

Solution

How to collect log files from Office Communicator, Lync, and Skype for Business Client

To create and collect log files from Office Communicator, Lync, or Skype for Business Client, follow these steps:

1.    Make sure that logging is enabled. To do this, use one of the following methods, as appropriate for your situation: