Internet Explorer Flickers within XenDesktop (and maybe XenApp too)

Now before you go “oh yeah, this is any easy one – you just need to enable Force Offscreen Composition, see this Citrix article http://support.citrix.com/article/CTX126186 or http://support.citrix.com/article/CTX118254 or http://support.citrix.com/article/CTX126216” what if you already have enabled this and you’re still getting flickering in IE???

Well, after a lot of delving around I found the following so I’m going to share it with you as it took me ages to find this.

In some circumstances, applying the Force Offscreen Composition reg key isn’t enough.  Now, this may be to do with XenApp 6.5 and XenDesktop 5.5 using Active Display, the successor to Progressive Display but I’m not entirely sure.

Anyway, it transpires that a Citrix client setting will resolve this.  You need to disable OnScreen Surface (OSS) setting.  This is done by making the editing the registry entry EnableOSS.  You will need to change this from “*” to “FALSE”.

EnableOSS can be found in the following key on the local machine:

HKEY_CURRENT_USER\Software\Citrix\ICA Client\Engine\Lockdown Profiles\All Regions\Lockdown\Virtual Channels\Thinwire Graphics

EnableOSS via the Registry
Now, this is all well and good but it is a per user setting.  If you want to set it globally and are using Web Interface then you’re in luck!  You need to edit the default.ica file for the specific webpage you are using. 

This can be found in C:\inetpub\wwwroot\citrix\[website-name]\conf\default.ica.  You will need to add the entry EnableOSS=False into the [Application] section (see below).

EnableOSS setting via Web Interface

 Not the most common issue you’ll come across but a nice little nugget to know when you’re wondering why IE is still flickering after setting Active Display and Force Offscreen composition!

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