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: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:
- 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
- Calendar and Free/Busy information from Outlook
- Exchange Web Services (EWS)
- Response Group Service
- Address Book Service
This issue occurs for multiple reasons, and in certain scenarios, it is the expected behavior. Lync generally prompts you for credentials only after you're signed in and when it must connect to an external service such as the Microsoft Exchange Free/Busy service or the Exchange Calendar service. If Lync continues to prompt you for credentials after it has done this several times, there's probably an issue with Outlook or with the Exchange services.