While logging in to Skype for Business/Lync client user may face one of the following errors:

Find the troubleshooting steps below:

Error:
Cannot sign in because the server is temporary unavailable.

Resolution:

  • Verify the user has Skype for Business service enabled. Navigate to CONTROL PANEL > Services > Skype for Business > verify that the box next to the user’s name is checked.
  • Verify the settings are correct: under Tools > Options > Advanced both internal and external servers are set up. You may find correct server addresses in CONTROL PANEL under Services > Skype for Business > Instructions > Server Name.

Error:
Can't sign in to Skype for Business/Lync. We're having trouble connecting to the server.

Resolution:

  • Verify the settings are correct: under Tools > Options > Advanced both internal and external servers are set up. You may find correct server addresses in CONTROL PANEL under Services > Skype for Business > Instructions > Server Name
  • Run Trace Route to the Skype for Business server. Read the Knowledge Base article on What Is A Trace Route (tracert)? How Do I Run One? for more information. You may find correct server addresses in CONTROL PANEL under Services > Skype for Business > Instructions > Server Name

    If there are some asterisks (*) or the response time is > 200 ms, locate the hop where it happens. You may need to reboot your router or modem or contact your ISP. If the asterisks appear beyond your Network, contact Support.

  • Check that Skype for Business ports and protocols are open and supported in your network. Read the Knowledge Base article on Ports And Protocols Used By Skype for Business/Lync Secure Chat And Conferencing for more information.
  • Replicate connection in a different environment (different machine and network). If the user is still not able to log in, contact support.
  • If a different machine/network worked, test with another network and another user on the same machine (e.g. connect the machine to Wi-Fi).  

    If users are able to connect through a different network, contact your local Network Administrator to resolve router/firewall/network configuration issues.

    If another user is not able to connect as well, contact your local administrator to resolve Windows/OSX core issues.

Error:
Skype for Business/Lync was unable to sign in. Please verify your logon credentials and try again.

Resolution: 

  • Verify you are using the correct username and password and are able to login to the Webmail.
  • Verify you are using mailbox UPN (not an alias). You may find the correct UPN in CONTROL PANEL under Users.
  • If you have recently changed UPN for a user, SIP address and SIP attributes may not match the new UPN. Contact support for a resolution.
  • Clear up Skype for Business/Lync cache.