Desktop or Application sharing can't connect in a Skype for Business Online conference


A user shares the user's desktop or an application with other participants through Skype for Business Online (formerly Lync Online). However, the participants in the conversation can't connect to the desktop sharing session. The user receives the following error message in Lync 2010 or Lync 2013:

Cannot start Desktop/Application Sharing due to network issues.

A message that resembles the following entry is recorded in the Lync UCCP logs:

ms-client-diagnostics: 23; reason="Call failed to establish due to a media connectivity failure when one endpoint is internal and the other is remote";CallerMediaDebug="application-sharing:ICEWarn=0x4000320,LocalSite=, LocalMR=,RemoteSite=, RemoteMR=, PortRange=1025:65000,LocalMRTCPPort=54829, RemoteMRTCPPort=51184,LocalLocation=1, RemoteLocation=2,FederationType=0"


To resolve this issue, follow these steps:

  1. Try to reproduce the issue by using one contact or multiple contacts. If the issue occurs for only one contact, determine whether anyone else can reproduce the issue with the same contact. If the issue occurs for multiple contacts, check for commonalities among the group of contacts.

  2. Important

    This step doesn't apply to Office 365 dedicated subscription plans. Don't use this step to troubleshoot this issue if you have an Office 365 dedicated plan.

    Make sure that your network meets all the requirements for the best experience with Skype for Business Online. For more information, go to the following Microsoft Knowledge Base article:

    2409256 You can't connect to Skype for Business Online, or certain features don't work, because an on-premises firewall blocks the connection

  3. Verify that the video drivers are up to date and are working correctly.

More information

This issue usually occurs because one or more of the following conditions are true:

  • Port 443 or ports 50040-50059 are blocked.
  • Traffic to or from is blocked.

If the error message in the "Symptoms" section is present in the UCCP client logs for Lync, there's likely a communication error between two Lync edge servers. This means that two users who try to connect are connected through different edge servers that can't communicate with one another.

For more information about logs for the Skype for Business desktop client, see Gathering Logs from a Skype for Business Desktop Client.

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