Can't share a PPT in Skype for Business 2016 when blocking legacy PowerPoint file formats

Symptoms

In the PowerPoint File Block Settings, you block opening or saving for PowerPoint 97-2003 Presentations, Shows, Templates, and Add-in Files. When you try to share a PowerPoint presentation in Microsoft Skype for Business 2016, even when an Office Online Server is used to present the file, the presentation fails.

Cause

Skype for Business, for compatibility with legacy clients, exports PowerPoint files by using this legacy format. When the format is blocked, the export fails. This causes the sharing process to fail.

Resolution

To fix this issue, install the October 6, 2020, update (KB4486669) for Microsoft Skype for Business 2016.

Important

Enabling this fix will break compatibility with Lync Server 2010 and earlier clients. Users can still join via the Skype for Business Web App if their client is not compatible.

To enable this fix, create a policy by using one of the following options:

1. Create the following registry key on the client computers:
   
   Root: HKEY_LOCAL_MACHINE or HKEY_CURRENT_USER
   

   Key: Software\Policies\Microsoft\Office\16.0\Lync
   

   Value Type: DWORD
   

   Value Name: DisableGenerationOfLegacyPPTFiles
   Value Data: 0x00000001
   

2. Create the following client policy entry by using the Skype for Business PowerShell:
   
   $x = New-CsClientPolicyEntry -Name "DisableGenerationOfLegacyPPTFiles" -Value "true"
   Set-CsClientPolicy -Identity "<ClientPolicyName>" -PolicyEntry @{Add=$x}