Lync Troubleshooting: Conferencing Invite Failed

Symptoms

While scheduling a Lync meeting, you see the message "Conferencing Invite Failed."

Resolution

If you run into issues scheduling invitations for an online meeting or conference call, contact your support team. To help them resolve the issue, check the following:

Does the issue have to do with scheduling meetings, or accepting the meeting invitations? It helps your support team if you can isolate the issue as having to do with scheduling or accepting meeting requests. Make sure each participant is not blocked from receiving conference invitations (for example, make sure any blocked or safe sender lists are properly configured.
If you can create conference invitations successfully but participants are not receiving them, then have participants check their Junk Folder for the invitation.
If the conference invitation is sent to participants using different versions of Lync or Communicator, then make sure participants install the latest version of the appropriate conferencing add-in.
Specify which application you are using for conferencing (for example, Lync or Lync Web App).
Make sure your phone or device is optimized for conferencing. A list of devices that are optimized for Lync is available on Microsoft TechNet at Phones and Devices Qualified for Microsoft Lync.
Specify which version of Lync or Communicator you and your participants are using. Some newer versions may not support or operate the same way as older versions.
Have participants confirm with their support teams that their networks and accounts support conferencing.
If you are having issues with scheduling an online meeting or conference call, try to join a different online meeting or conference call first. Or if you are having issues with joining, try scheduling. It helps your support team if you can isolate the issue as having to do with scheduling or joining.
If you are having issues with scheduling, see if others can schedule online meetings and conference calls. If no one can schedule or join conferences, then the issue is likely related to network connectivity (for example, there may be an intermittent issue or temporary network outage).
If you are conferencing with external contacts, contact your support team to make sure that your account is enterprise voice (EV) enabled.