I have recently come across an issue with HDX Flash Redirection in a few customers environments.  The issue would cause Internet Explorer to completely lockup in an HDX/ICA connection to the desktop.  In this blog post, I am going to go over what I have seen around this issue and the possible workarounds and fixes.

What is the issue?

Internet Explorer can lockup when going to a site with Flash content.  No matter what the size of the Flash content is, Internet Explorer will lockup.  I have seen the most lockups with small Flash banners.  You can continue to work in the virtual desktop, but Internet Explorer is unusable until you end the process in Task Manager.  I have seen the issue on Windows 7 virtual desktops with Internet Explorer 8 running on XenDesktop 5.5 when using the Receiver 3.0 and Receiver 3.1.  There are reports in the Citrix Support Forums that the issue also happens with Internet Explorer 9.  Windows XP and XenApp 6.5 have also be reported to have the issue.  You can view the Citrix Support Forums post here – Receiver 3.0 and IE 8 Behavior and HDX and IE8 Freezing/Crashing.  I have tested XenApp 6.5 and XenDesktop 5.5 but was only able to reproduce the issue on Windows 7 with Internet Explorer 8 in XenDesktop 5.5 when connecting with the Receiver 3.0 or Receiver 3.1.  I have not tested Windows XP or Internet Explorer 9.

You can connect to the same virtual machine while Internet Explorer is locked up with a Remote Desktop Connection and Internet Explorer will work fine.  You also connect to the virtual machine console while Internet Explorer is locked up and Internet Explorer will work fine.

What are the workarounds?

The workarounds I have tested and confirmed that work are:

  • Downgrade from Receiver 3.0 or Receiver 3.1 to Online Plug-in 12.x
  • Downgrade the XenDesktop VDA to 5/5 SP1
  • Create the UseAudioSyncing (DWord with value 0) Registry Key in HLKMSoftwareCitrixHDXMediaStreamForFlashServer for 32bit or HLKMSoftwareWow6432nodeCitrixHDXMediaStreamForFlashServer for 64bit
  • Disable Flash Redirection – Internet Explorer would pause for a few seconds but still works

What is the fix?

Citrix support has confirmed this is a bug and they are working on a hotfix to fix the issue.  You can open a support case with Citrix support and get a private hotfix to address the issue.  If you open a case, request private hotfix# LA0691.  I have opened a support case myself with Citrix and received the private hotfix.  I can confirm the private hotfix has fixed the issue (so far no reports after a week when issue was happening every day) at the customers I have come across the issue at.  I have also not been able to reproduce the issue in my tests after installing the hotfix in my test environment.

If you have found this article interesting or if you have any other insights, please feel free to contact me via email.