Microsoft Lync 2010 continuously asks for credentials after signing in

When you try to access Microsoft Lync Online by using Microsoft Lync 2010, you are repeatedly prompted to provide a user name and a password.

This issue can occur for multiple reasons, and in certain scenarios, this is expected behavior. Lync generally only prompts you for credentials after you are logged in when it must connect Lync to a linked service such as the Microsoft Exchange Free/Busy service or the Calendar service.

In most cases, if Lync does prompt you for credentials, Lync prompts you three times to connect to various Exchange Web Services. If Lync continues to ask for credentials after three separate dialog prompts, there is likely an issue with Outlook integration or with the Exchange services themselves.

If you try to use a federated account on a domain-joined computer that is logged into a network, the credentials should be detected automatically. However, if you are prompted, enter the credentials as follows:

• Sign-In Address: username@domain.com
• Username: username@domain.com

Lync will generally prompt for the following reasons:

• Outlook integration is not functioning correctly.
• The Exchange Server or the mailbox is unavailable.
• Exchange Web Services are inaccessible.
• A proxy or firewall is blocking ports that Microsoft Lync has to have open to connect to Exchange Web Services.

To resolve this issue, run Office 365 Desktop Setup to configure both Outlook and Lync. Then, consider the follow scenarios.

Outlook integration failure

If Lync does not integrate automatically with Outlook, Lync prompts for credentials to be able to connect with your Exchange mailbox.

For more information about how to resolve typical Outlook integration errors, click the following article number to view the article in the Microsoft Knowledge Base: Exchange Server or Exchange Web Services is unavailable

If Exchange Server or Exchange Web Services is unavailable, this causes Lync to continuously ask for credentials because Lync cannot contact Exchange for authentication. To resolve this issue, verify that Outlook has connectivity to the mailbox. And, if Outlook cannot connect to Exchange, troubleshoot the issue as an Exchange connectivity issue.

Another way to determine whether Exchange Web Services is down is to see whether Outlook can connect to the Free/Busy service. To validate this connectivity, create a new meeting invitation, invite several attendees, and use the Scheduling Assistant to see their Free/Busy status. If Exchange Web Services is down, the Scheduling Assistant indicates that the status information is unavailable for all the attendees.

Proxy or firewall blocking issues

If a firewall or a proxy is blocking Lync from connecting to the Exchange Web Services, you may experience symptoms such as credential prompts, stale ABS, and intermittent free/busy presence issues. To resolve this, verify that the user has the correct proxy configured in Windows Internet Explorer. To do this in Internet Explorer, click Tools, click Internet Options, click Connections, and then click LAN Settings.

Ports 443, 5060, and 5061 must be open on the firewall and on proxy servers to enable traffic to pass freely.

For more information about firewall or proxy issues in an Office 365 environment, click the following article number to view the article in the Microsoft Knowledge Base: