Skype for Business login issue with Certificate error

By | December 18, 2019

Sometime skype for business may not sign-in and give the following error.

Solutions to fix Skype sign-in certificate issue

1. Delete the sign-in info

On the Skype for Business sign-in window, click Delete my-sign in information

This deletes your saved password, certificates, and connection settings

Next, you have to input the account info and see if you can log in.


2. Flush DNS cache

Open Command Prompt (Run as Administrator) > type the following command and press Enter:
ipconfig /flushdns

Wait until the process completes and then close CMD.


Windows 10 Firewall might be blocking Skype as well. Learn how to unblock it here.


3. Make changes through the Registry Editor

  1. Press the Windows logo key + R on your keyboard > type regedit and hit Enter to open the Registry Editor
  2. Find the following registry path: HKEY_LOCAL_MACHINESOFTWAREMicrosoftCryptographyMachineGuid
  • Double click on MachineGuid > if the value contains a list of numbers and letters in brackets – e.g. {c1cbd94c-0d35-414c-89ef-dd092b984883} – delete it
  • Close the Registry Editor > restart Lync and try signing-in to Skype for Business.

4. Perform some troubleshooting steps for Lync 2010 and Lync 2013

If you’re still using Lync, here is how you can fix this problem:

  1. Locate the app data folder: %LOCALAPPDATA%MicrosoftCommunicator<sip_address@contoso.com
  2. Delete the folder containing information associated with your email address

Restart Lync and try to sign-in using Skype for Business

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