Looking at the Event Log in vCenter against the host you see the error below as the job eventually fails against the host…but remains in progress in the Web Client. Restarting the NSX Manager, the Hosts or the Web Client services doesn’t stop the progress. To reset the NSX Web Client Status and stop it thinking that the VIB deployments are still in progress you need to kill the install job from the ESX Agent Manager (thanks @santinidaniel) and get the opportunity to Resolve/Uninstall the host modules again.
Once you get past the spinning you will see a failure and you will get an error message similar as highlighted below:
VIB module for agent is not installed on host <hostname> (_VCNS_xxx_Cluster_VMware Network Fabri)
This error is detailed in a couple of forum posts and in a VMwareKB here. You can try and do a manual NSX Module install however as the KB suggests the problem more than likely lies with Update Manager. In my specific case the Update Manager wasn’t happy with a recent vCenter SSL Certificate Upgrade and required a repair to allow the new SSL cert.
Once Update Manager was sorted the Host Preparation Tasks went through without issue and we where on our way. Point and case here is that you should never forget about the supporting infrastructure…even in Nested Lab environments. Know your dependencies and requirements and ensure they are all in working order…can save you some headaches along the way.