One of our accounts unable to sign in to Lync

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We've been using office 365 for some time with our small business of 9 employees.  Despite the fact that we only have 9 employees, we have 14 active 365 accounts, for video conferencing across the country, a jobs email account, etc etc.


In any case, 13 of these accounts work perfectly when it comes to Lync, but one of them does not.  Even with the correct password, the service comes back with "Lync was unable to sign in.  Please verify your logon credentials and try again.  If the problem continues, please contact your support team".  This occurs on many different computers, both Mac and PC, and we use manual configuration of internal/external server names being 


Using the same password, we are able to sign in to the portal.  Using admin credentials, it definitely labels that particular license as having access to Lync Online (P1). 


This may be nothing, but when I click to sign into this particular account, the "thinking donut" fakes me out and I always "think" it's going to sign me in, but then it just starts spinning again and comes back with the same "verify logon credentials and try again" error.  Does anyone know of a possible known issue here? 




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  • Hi Neilo,

    We too recieve this same error when an particular user attempt to sign in to the Lync online.

    This Error may occur when the user’s root certificate is corrupted or is out of date.

     This can be resolved by simply deleting the sip_ sign in name and the EndPoint Configuration.Cache.

    C: \user\<username>\appdata\local\microsoft\communicator\sip_<sign in name>

    For e.g. C:\Users\Computer1\AppData\Local\Microsoft\Communicator\

    Thanks and Regards,

    Surya Begum.

  • Hi Surya,

    Thanks for your efforts and suggestion on this issue.



    Hi Neil,

    Thanks for posting here.
    I understand 1 user in your company experienced the log-in issue and others can log in Lync Online successfully. You have tried to use several different computers, and the connectivity issue persists.

    Based on the current situation, to help us narrow down this issue, would you please perform the following troubleshooting steps?

    Step 1. Try to use another user credential to log in to Lync Online with the same computer and see if the user experienced the same log-in issue.

    If this does not help, have the account used successfully before? If so, you may also renew the user account certificate in Windows Certificate Manager and check the status of this issue as Surya suggested.

    To renew a user account certificate, follow these steps:
     a. Open Windows Certificate Manager. To do this, click Start, click Run, type certmgr.msc, and then click OK.
     b. Expand Personal, and then expand Certificates.
     c. Sort by the Issued By column, and then look for a certificate that is issued by Communications Server.
     d. Verify that the certificate is present and that it is not expired.
     e. Delete the certificate and try to sign in to Lync Online.


    Grace Shi

  • Thank you very much for the response.  In regard to step 1: Yes, I use another account for Lync on this computer very often.  I tried 3 of our accounts on this computer, and the problem account is the only one that doesn't work.  My peer tried the same thing on his windows machine to no avail as well.

    In regard to step 2: I tried this twice (just to be sure), but it didn't seem to work either.  Great suggestion though, it made a lot of sense to me.

    As far as Surya's suggestion is concerned, there is no certificate on any of the computers for that particular account; none of us have been able to sign into it ever.  Additionally, I was only able to check this on a Windows machine; we are mostly Mac users in this office, and this issue occurs on both platforms.

  • Hi Neil,

    Thanks for your update.
    As others can sign in Lync Online on this computer successfully, this log-in issue should be happened on your account. To further narrow down this issue, would you please check if the user’s UPN matches the SIP address.
    To verify the user’s UPN and SIP addresses are correct, please see this article:

    Besides, the particular user's sign-in address is using your custom domain or the original domain.

    Grace Shi

  • Hi Neil,

    How are things going? Is there any update on the status of the issue?

    Grace Shi