Lync Server 2010
Exchange Server 2010

This morning, some of my Lync 2010 and 2013 clients began receiving this error in Lync:

"Exchange needs your credentials. Until then, you might see outdated info in Lync. [Enter Credentials]"

I have tried:

1. Re-entering credentials.
2. Deleting all saved credentials on the client computer.
3. Deleting saved user certificates from the Lync server.
4. Restarting the Lync client.

I've seen discussions in which people in a mixed Exchange 2007/2010 organization saw this error, but not in a pure 2010 organization.

Any other ideas of what to lo

Hi reprac,

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. 

And theres a related KB for your reference.

http://support.microsoft.com/kb/2298541

Best regards,

Eric

I was going to say we aren't having any problems with Exchange or Outlook, but this morning users are now reporting a similar login prompt from Outlook. It doesn't accept any login credentials, but if they cancel it, Outlook connects anyway.

Problem resolved. The cause was a custom autodiscover config that was inadvertently overwritten.

Can you please explain the steps that you did.The solution is too generic - "custom autodiscover config"

I can give you a little more information, but I'm not sure it will help you.

We host multiple organizations on our Exchange and Lync servers. All users log in using username@domain.com, but their default reply-to address could be anything. One of our accepted email domains (call it intrelay.com) is configured in Exchange as an Internal Relay domain as it is shared by several other Exchange organizations that have no trust relationship with us or intrelay.com. (Sound confusing? It is.)

When the email client of one of our users send an autodiscover request, it sends it to their default reply-to address domain. In order to accomodate Lync and other autodiscover clients in this crazy domain sharing setup  Intrelay.com has set up a custom service that looks up the email address in a database and then redirects the autodiscover request to the appropriate Exchange organization depending on which one the user actually belongs to. Intrelay.com inadvertently disabled the redirection so that autodiscover was sending all of our customers who use intrelay.com email addresses to the wrong server for client config information.

The solution was for intrelay.com to re-enable the user-lookup-redirection. Unfortunately, I can't tell you anything about how the redirection works because I don't know.