This article describes the fix for the Skype for Business/Lync Attendee error that external contacts receive when they try to connect.

The scenario of the issue:

  1. Skype for Business user initiates a meeting and invites an external contact.
  2. External contact tries to connect via Skype for Business/Lync Attendee, but receives the following error:
    Cannot sign in becasue the server is temporarily unavailable. Reference error ID 28 (source ID 238)
    Cannot sign in the Skype for Business/Lync Attendee because of a problem connecting to the server. Reference error ID 102 (source ID 238)

To fix the connection:

  • Create a SRV record for your domain. For instance, if user@yourdomain.com invites contact@otherdomain.net the SRV record should be created for yourdomain.com.
    You may need to contact your DNS provider to add this record.

Syntax of SRV record:

  • Service: _sip
  • Protocol: _tls
  • Port number: 5061
  • Host: lyncsip.XX.XX.XX. For instance, lyncsip.exch0XX.serverdata.net.
    You can find the correct setting in CONTROL PANEL > Services > Skype for Business > Instructions.
  • Priority and weight can be left 0.

To verify the record is created successfully and propagated:

  1. Navigate to Start, find Cmd and open it.
  2. Type the following lines one by one and hit ENTER after each:
    Note: If you do not know someDNSserverIP you may use 8.8.8.8


    nslookup - someDNSserverIP
     

    ENTER

    set q=SRV
    ENTER

    _sip._tls.yourdomain.com
    ENTER
  3. The results should look like this:
     priority = 0
     weight = 0
     port = 5061
     srv hostname = lyncsip.XX.XX.XX