View Administrator experienced a strange issue not long before a scheduled upgrade to Horizon 6. Each time Composer attempted to spin up a new desktop, the task would error out in vCenter with the error The resource ‘104’ is in use. One would think that this issue would not have much impact. Unfortunately, this issue wreaked havoc on a linked clone pool. Over a thousand errors were reported in View Administrator overnight when this issue arose, as the desktop pool was not set to Stop provisioning on error. Upon refreshing the ports on the vSwitch, the error went away.
A quick search turned up a VMware KB article discussing that the number 104 refers to a specific port on the virtual distributed switch. Looking at the ports on the virtual distributed switch, it was observed that an older version of a template that was once servicing a full clone pool was occupying the port in question. There seemed to be some sort of confusion on the side of vCenter. Errors like this had been solved in the past by rebooting vCenter. The next outage window available for a vCenter reboot was allocated for the upgrade window. Since the first step in the upgrade was to reboot vCenter, this seemed like a good time. After the reboot of vCenter, and a successful upgrade the issue persisted.
It was time to look at the template. Since the template was an older version of the standard desktop that was kept around for fallback purposes, it was determined that a good first step was to convert the template to a virtual machine, and disconnect it from the vDS. Upon right-clicking on the template, it was discovered that the option to Convert to Virtual Machine was grayed out. A quick search returned the VMware KB article discussing possible permissions issues. Since permissions were not the case, the article recommended removing the VM from inventory. Removing the template from inventory fixed the problem, and it has yet to return. Rather than re-add the VM to inventory, the VM was deleted, as it was no longer in use.