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Citrix Virtual Apps and Desktops 1912: Session Prepare Failure

Adri Hofste


Hi there,


Each day random users (about 5-10 on a total of 800) are unable to reconnect to their Windows 10 VDI. Director shows multiple client configuration errors for the user and a session prepare failure for the VM they are reconnecting to. 


Eventviewer on DC's show event id's 1039 and 1116:


The Citrix Broker Service failed to contact virtual machine 'XXXXX' (IP address YYYYYYY). 
Check that the virtual machine can be contacted from the controller and that any firewall on the virtual machine allows connections from the controller. See Citrix Knowledge Base article CTX126992. 
Error details: 
Exception 'There was no endpoint listening at http://XXXXX/Citrix/VirtualDesktopAgent/ILaunch that could accept the message. This is often caused by an incorrect address or SOAP action. See InnerException, if present, for more details.' of type 'System.ServiceModel.EndpointNotFoundException'.



The Citrix Broker Service failed to broker a connection for user 'XXXXX'' to resource 'DesktopX'. A communication error occurred when attempting to prepare the virtual machine 'XXXXXXl'. 
If the problem persists, please restart the virtual machine, but note that unsaved data may be lost. 
Error details: 
Exception 'There was no endpoint listening at http://XXXXX/Citrix/VirtualDesktopAgent/ILaunch that could accept the message. This is often caused by an incorrect address or SOAP action. See InnerException, if present, for more details.' of type 'System.ServiceModel.EndpointNotFoundException'.


The VM becomes unresponsive and can only be repaired by a forced reboot.



Citrix Hypervisor 8.1

Citrix Virtual Apps and Desktops 1912

PVS 1912

Storefront 7.15 CU5


Any idea what could be the problem here?


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8 answers to this question

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  • 0

Hi, we are facing the same situation. 


7.15 CU4..


This erros appears randomly. 1x p/day. We have 10 VMS to Session Apps (xenapps) with MCS. 

After this, machine gets unresponsible with session named (3) logged.

we need to restart entire vm. 


I suspect the problem source could be our vmware host, but i dont know go deep to analyse this.




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Make it another person experiencing it.


1912CU1 DDC's/PVS

7.15CU4 Storefront

1912CU1 and 7.15CU4 VDA's

vmware 6.7 (tools 11269 on VDAs)

Latest August Windows Updates. 

App Layering 20.05


I have over 1000 VDI's and probably somewhere around 20-30 people experiencing this each day.  


Going to roll back the OS layer to mid July before the issue cropped up and see what kind of differences I can find. 

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You can search in the StoreFront Events to search what happen. Maybe this can help "https://support.citrix.com/article/CTX261747".
Also check:
.- Time synchronization VDA and Controller need to have the same time, you can see if VDA change time in event logs when fails.
.- If you have more than one network adapter, force comunication for one of them with routes. IF you are using 1 adapter for network and the other for streaming, validate that the streaming adapter doesen't have default GW.
.- Verify StoreFront events

If everithing looks ok, then install wireshark in your VDA and make a packet capture, you can attach it and lets see what's happening when the agent fails.

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  • 0
  • Time in sync. 
  • One network adapter
  • No storefront Errors that can be found.
  • Errors can be found on the DDC's and the VDA.  Just looks like there's a problem opening the connection again.  Ran around with cyber and network teams to see if there was anything in the way and got nowhere on that front. 

Wireshark doesn't really work with App Layering last I checked.  I can obviously force it in there by opening the vdisk in private mode after the build, but trying to roll back first so my users stop escalating tickets to me.  If I fail to get it working after the rollback, I'll open up a ticket with support.

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Did a lot of image building/testing today. 


  • Rolled back OS Layer, Platform Layer, and Office layer.  Built new images and it didn't have any affect on the issue.
  • While troubleshooting another issue, the App Layering support team instructed me to update ELM from 1908 to 2005 around the time this started.  They also gave me a 1908 driver package that could be used to swap drivers in ELM when images are built.  I rebuilt an image with the 1908 drivers in place on ELM 2005.  Now I can not replicate the reconnection issue, however, I also can't connect the existing user layers because they've been upgraded by the 2005 drivers in images that are in production. 
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I found a few more things that may help some of you.  

1. This seems to be happening more frequently with EDT/HDX Adaptive Transport turned on.  When we disable it the issue is less frequent.

2. In some instances our VDAs cannot be rebooted and must be powered down.  I have found that killing GfxMgr.exe in the task manager allows me to reboot the machine instead of power it down.

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I was able to get the app layering support team to send me the 2003 drivers as well and perform a driver swap in ELM.  Rebuilt an image from template with the 2003 drivers in place and had no issues with that one.  User layer was able to be attached just fine.


Just for kicks, I swapped drivers back to 2005 package and built an image with the exact same template and was instantly able to recreate the issue.  Going to see about transferring my case to the AL team. 

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