Product Documentation

Known issues

Oct 16, 2017

General known issues


Editing the registry incorrectly can cause serious problems that may require you to reinstall your operating system. Citrix cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. Be sure to back up the registry before you edit it.

  • Simulcast does not support H.264 hardware encoding capabilities of UVC cameras.


  • When starting an audio point-to-point call and starting video at the same time, a Cannot start video message appears. 

    Workaround: Do not start an audio point-to-point call and video at the same time.


  • When an external Optimization Pack client starts a point-to-point call to an internal Optimization Pack client, the video quality on the internal client might be poor. 

    Workaround: Limit the size of your video window by keeping the requested resolution below 960 x 720.


  • In point-to-point calls using a UVC camera, or in a Meet Now, before a user starts transmitting video, the aspect ratio of the picture-in-picture video window might not display in the correct aspect ratio. On point-to-point calls, the video you're sending might be wider and include more content than what is visible in the picture-in-picture window. In Meet Now, after each participant becomes an active speaker, the aspect ratio changes to 16:9.


  • AMD hardware acceleration endpoints might fail to send and receive video in a Meet Now with a Lync online Office 365 user.


  • When endpoints are using AMD chipsets and hardware accelerated decoding, users might see short periods of black incoming video and accelerated incoming video playback after resizing the conversation window.


  • Audio might be distorted when CPU usage is high, especially in fallback mode.


  • Maximizing the video window on low-end clients increases CPU usage, which might cause audio problems.

    Workaround: Do not enlarge your video window.


  • We do not support two or more active network interfaces. For example, user1 has wired Ethernet and Wi-Fi enabled. User2 calls user 1 and connection problems occur causing the call to fail.


  • Optimization Pack 2.2.x is not compatible with the Polycom RealPresence Trio 8800. If you use the Skype for Business UI to accept a call, but use the Polycom RealPresence Trio 88 to hang up the call, the call doesn't end.

  • After the called party using a IP phone accepts a video call as audio-only, the caller cannot add a third participant to turn this into a conference call. Workaround: The called party can add the third participant, after which all conferencing capabilities are available. 


  • In some cases on Linux, the self-view picture might display only a corner portion of the full video. 

    Workaround: Resize the video conversation window.

  • If a user on Mac OS X changes the dock UI setting while Skype for Business is running, current and future calls do not display local or remote video. 

    Workaround: Restart Skype for Business.


  • On team calls with Simultaneous Ringing set, a call disconnect might occur when someone else picks up the call. If you observe this issue, supply log files to Citrix Technical Support.

  • If a caller plugs in another human interface device (HID) during an active call, the call might drop.


  • Skype for Business might crash at startup after RealTime Connector is installed.

    Workaround:  Restart Skype for Business.  


  • Some headset devices (for example, Polycom and Plantronics) are mistaken for speaker phone or handset devices. 

    Workaround: Restart Skype for Business


  • If Citrix Receiver for Mac 12.0 is on the endpoint device and a Human Interface Device (HID) is removed after Skype for Business and RealTime Optimization Pack are running, the RealTime Media Engine might crash.

    Workaround: Upgrade your version of Citrix Receiver for Mac to a more recent version.


  • Skype for Business might crash when exiting a video conference call or when exiting from the notification area.

    [#612444, #612115, #610894]

  • Optimization Pack, does not appear in the Citrix Receiver for Windows Support Info generated from the Advanced Preferences menu.

    [#608200, LOP-650]

  • When a public switched telephone network (PSTN) gateway is configured to generate custom ringback tones, the Skype for Business built-in ringback tone might be heard for a short period before the gateway ringback is heard.

    [# LOP-1243]

  • When fallback mode is set to audio only, and the users in fallback mode participate in a video conference, they might see their own states in the participant list displayed incorrectly as On Hold. Other users are not affected.


HDX RealTime Media Engine known issues

  • The RealTime Media Engine v2.0.5 causes a slideshow effect in conference video calls when interoperating with 2.1.X through 2.3.X 

    Workaround: Disable H264UC codec:
    Add DWORD DisableH264UC in the registry:[HKEY_CURRENT_USER\Software\Citrix\HDXRTConnector\MediaEngine\CodecSettings]
    The codec is enabled if the value is absent or set to 0, and is disabled if the value is present and set to 1.


  • When a user (user2) on a Mac tries to use the RealTime Media Engine that another user (user1) installed, user2 might not receive an optimized experience.

    Workaround: On a Mac, install the RealTime Media Engine by using the actual user's logon.

  • For Citrix Receiver for Windows versions  4.2 and earlier - Uninstalling the Citrix Receiver, uninstalls HDX Real Time Media Engine. You must reinstall HDX Real Time Media Engine after installing Receiver. For more information, see


  • Sometimes, when attempting to install HDX RealTime Media Engine on Windows, a message indicates that there is no available disk space. However, limited space does exist on the Z:/ drive of the terminal. This is a known issue for Microsoft installers and applies to Citrix Receiver as well.

  • During installation or un-installation, it is possible to encounter certain error conditions where the error message string is not localized.

    [#14530, #93]

  • In Seamless mode, the following issues exist for Full Screen video:
    • Full Screen video appears in letterbox format with the Linux version of the RealTime Media Engine in Seamless mode.


    • The Full Screen Control hides behind other apps in a Seamless session in XenApp Seamless mode.


Third party issues

  • The Windows 10 Anniversary Update has issues with web cameras and H.264 that might cause unnecessary bitrate adaption problems in RealTime Optimization Pack to RealTime Optimization Pack video calls. The problem is constant video resolution changes on your Windows 10 endpoints. 

    Workaround: Add this registry key to the Windows 10 endpoint.

[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows Media Foundation\Platform]


  • RealTime Connector on 64-bit Windows might crash or become unstable if Microsoft .NET Framework 4.6 is installed with default configuration. For possible workarounds, see RyuJIT settings cause managed applications to crash after you install Microsoft .NET Framework 4.6.


  • There might be problem dialing dual tone multi frequency (DTMF) digits using a Jabra Pro 9465 device on a Linux client.

    Workaround: Use the RealTime Optimization Pack interface to dial the DTMF digits.


  • Citrix RealTime Optimization Pack does not support the Plantronics Clarity P340 audio device but does support the P340-M (Skype for Business qualified device).

    [#597048, 603639, 608218]

  • On Mac OS X, Citrix RealTime Optimization Pack does not support Hewlett-Packard 4310, Hewlett-Packard 2300, and Microsoft LifeCam Studio webcams for point to point calls.


  • Linux might mistake some audio devices containing buttons for a Human Interface Device (mouse) instead of an audio device. When a user presses a button, Linux interprets it as a mouse button press and prevents the regular mouse from working correctly until the call is terminated.

    Workaround: Configure the Linux X11 graphics subsystem to ignore the devices as sources of user input by creating or modifying a .conf file in the /usr/share/X11/xorg.conf.d directory with the following sections (for example, Jabra, Plantronics, or Sennheiser). 

Section "InputClass"
Identifier "Jabra"
MatchVendor "Jabra"
Option "Ignore" "True"

Section "InputClass"
Identifier "Plantronics"
MatchVendor "Plantronics"
Option "Ignore" "true"

Section "InputClass"
Identifier "Sennheiser"
MatchVendor "Sennheiser|1395"
Option "Ignore" "true"


  • The microphone volume level of some Linux clients is low.

Workaround: Increase the microphone level using the Linux system volume control.

  • The microphone volume level of the Polycom CX100 speakerphone is very low even at its full level when used with the HP Thin Pro client.

Workaround: You can modify the registry key that comes with the HP Thin Pro comes by using the regeditor program on the client, which can be run as root, or from the Registry Editor component of the Profile editor.

These settings limit the range of available settings on the input volume slider.  The RecordScale default value of 100 limits it to 25% of its maximum value for the microphone jack.  Setting RecordScale to the maximum value of 400 allows the slider access to the entire scale.


Value name: RecordScale
Value data: 400 (Default is 100)

Value name: RecordScaleAuto -
Value data: 0 (Default is 1- sets to 100)

1         Sets RecordScale value based on  hardware type.

2         Does not set RecordScale value based on hardware type.

For playback, these controls work the same way as the input volume controls.


Value name: OutputScale
Value data: 400 (Default is 100)

Value name: OutputScaleAuto
Value data: 0 (Default is 1)


  • You might encounter errors with Skype (not Skype for Business) on iOS 9.2.

    Workaround: Upgrade to iOS 9.3.2


  • If you have more than one camera connected to an endpoint and you want to use the second camera for videos or video previews, open Tools > Video Device Settings and select the camera and click OK.


  • If Skype (not Skype for Business) fails to connect video from the RealTime Optimization Pack in a video call, you might see a black screen or a still video from the RealTime Optimization Pack user.