Opening MMS via a URL in Windows Media Player on Citrix XenApp 6.5

I was configuring a Citrix XenApp 6.5 farm and we created some instruction video’s for the users to get used to the new interface and structure, we offered those video’s (*.wmv) via a URL on a streaming server via MMS. So far so good but when clicking on the button linking to the wmv’s files the wmv’s wouldn’t start. Apparently this is a common problem because Citrix released a kb article on it: Citrix XenApp 6 is Unable to Open MMS Files

The title says Citrix XenApp 6 but when looking at the article it says:

This document applies to:

XenApp 6.0 for Windows Server 2008 R2

XenApp 6.5 for Windows Server 2008 R2

So I changed to following key:


From: %programfiles(x86)%\windows media player\wmplayer.exe” “%l”
To    :“c:\program files (x86)\windows media player\wmplayer.exe” “%l”

After a reboot of the server, when I tried to start the vmw’s I got the following error:

citrix xenapp


I figured it would be something to configure with Attachment Manager as explained here: Description of how the Attachment Manager works in Microsoft Windows

But after configuring the proper options I still would get this error. So I went searching on the internet and found a topic op the VMware forums saying you could disable the warning by creating a key:

Created registry key:  [HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer\ProtocolExecute\horizon]

Created DWORD called “WarnOnOpen” and set value to “00000000”

Based on this key I tried to create the following key:


With a DWORD called WarnOnOpen with the value “00000000”

And after a reboot I was able to open the WMV without any warnings improving the user experience.


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Kees Baggerman

Kees Baggerman is a Staff Solutions Architect for End User Computing at Nutanix. Kees has driven numerous Microsoft and Citrix, and RES infrastructures functional/technical designs, migrations, implementations engagements over the years.

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