Error message when you try to sign in to Lync 2010 after a network outage or a Lync Online service outage: "Cannot sign in to Lync"

When you try to sign in to Microsoft Lync 2010 after a network outage or a Microsoft Lync Online service outage, you receive the following error message:

When Lync 2010 connects to a specific front-end server, it caches that endpoint to make the sign-in process faster in the future. However, sometimes the endpoint can be changed. This can cause sign-in to fail.

To resolve this issue, follow these steps:

Step 1: Update Lync 2010

Update Lync 2010. To do this, visit the Microsoft Update website, and then install any updates that are available for Lync 2010. Updates are available for Lync 2010 that prevent this issue.�

If the issue is not resolved after you update Lync 2010, go to step 2.

Step 2: Refresh Lync cached endpoints

To have us refresh Lync cached endpoints for you, go to the "Fix it for me" section. If you prefer to refresh Lync cached endpoints yourself, go to the "Let me fix it myself" section.


Fix it for me

To refresh Lync cached endpoints automatically, click the Fix it button or link. Then, click�Run in the File Download dialog box, and follow the steps in the Fix it wizard.




Notes

• This wizard may be in English only. However, the automatic fix works for all language versions of Windows.�
• If you are not on the computer that has the problem, save the Fix it solution to a flash drive or a CD, and then run the Fix it solution on the computer that has the problem.

Then, go to the "Did this fix the problem?" section.



Let me fix it myself

When Lync 2010 connects to a specific front-end server, it caches that endpoint to make the sign-in process faster in the future. However, sometimes the endpoint can be changed. This can cause sign-in to fail. To delete the endpoint cache, follow these steps:

1. Locate the local application data folder:
   • Windows Vista and Windows 7: %LOCALAPPDATA%\Microsoft\Communicator\<sip_address@contoso.com>\
   • Windows XP: %USERPROFILE%\Local Settings\Application Data\Microsoft\Communicator\<sip_address@contoso.com>\
2. Delete the file that is named EndpointConfiguration.CACHE.
3. Restart Lync 2010, and then try to sign in to Lync Online.

Did this fix the problem?

• Check whether the problem is fixed.
  • If the problem is fixed, you are finished with these steps.
  • If the problem is not fixed, see the following article in the Microsoft Knowledge Base article for additional troubleshooting steps:
    2541980� �How to troubleshoot sign-in issues in Lync Online�
    If the problem is still not fixed, visit the Office 365 Community website or contact support.
• We would appreciate your feedback. To provide feedback or to report any issues with this solution, please leave a comment on the "Fix it for me" blog or send us an email message.