Obscure Skype for Business desktop sharing issue

A colleague of mine reported an issue with Skype for Business where he was unable to either share his screen (or application or PowerPoint presentation), nor could others share their screens with him.

From the user’s side, clicking on the Present¬†button allowed him to toggle what he wanted to share, which would appear to work – the border indicated “connecting” while the recipient(s) waited for the presentation to begin.¬†After 30-40 seconds, the presentation error (…”the invitation has expired”) and time out.

If you encounter this issue, you can try the following registry hack, which worked for me:

  1. Open Regedit as an administrator
  2. Navigate to:
    HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
  3. Add the following DWORD and value:
    MaxUserPort=0000x3a98 (15000)
  4. Reboot for the changes to take effect.

You can find more information about MaxUserPort and other TCP/IP registry settings here. This issue seems to be newly introduced with Windows 10 version 1809.