In a new mission, I had to learn a new environment based on Citrix XenDesktop 4, Provisioning Services 5.6 and vmware vSphere 4.1. This week, I had a weird issue, I didn't change anything, I just didn't understood why suddenly VMs stopped to be available, in fact VMs were available but for some reason, it was impossible for everyone to access it through the Web Interface. VMs were working well XenDesktop brokers were fine Web Interface was ok Citrix License Server was up and running with correct license vmware vSphere was ok as well, VMs were running without any problem on it On the Web Interface, the following message was display while trying to launch a XenDesktop virtual desktop : "xxxxx is currently unavailable. try reconnecting and, if the problem persists, contact your administrator." On the DDC, XenDesktop Desktop Delivery Controller, I found event logs with ID 1301, source : Citrix Desktop Delivery Controller, with the following description : "The delivery controller failed to broker a connection for user xxxxx to desktop group yyyyy. The delivery controller cannot find any available virtual desktops. Please add more virtual desktops to the desktops group. If the problem is due to existing virtual desktops not becoming available, refer to Citrix Knowledge Base article CTX117248 for further information." It look like a communication problem between XenDesktop DDCs and vmware Virtual Center, so I checked every component, DDCs, Virtual Center.... I found nothing really relevant. So the next step was to enable extended logs on the DDC side, after a short search on Citrix website I found how to do do with CTX117452. I got a lot of logs, but after one day scratching my head to try to understand why without changing anything I had such behavior, I just had bunch of logs but I was missing something... Here is a short part of the pool_log.log file : I also took a log in the virtual desktops pool properties to check if everything was alright... It wasn't :   All the VMs within the Citrix Delivery Service Console were disassociated with Active Directory and a message confirm I had communication problem between vmware Virtual Center and Citrix XenDesktop : "Virtual machines could not be retrieved from the hosting infrastructure" and then a pop-up saying : "Error occurred whilst validating the list of virtual desktops. For more information about each error, hover the mouse over…