When installing service deployments such as Guest Introspection through NSX Manager the installation fails. The host task displays error Cannot complete the operation. See the event log for details.
The event log displays error event.com.vmware.vim.eam.issue.vibNotInstalled.fullFormat.
The service deployment shows the error Agent VIB module cannot be detected on the host. This may be due to a pending reboot on the host due to an earlier operation. Please check for any errors on the vCenter console of host that may be causing this. Resolving this error will attempt to install the VIB on the host again.
If an instance of Update Manager is registered with the same vCenter Server as NSX Manager then Update Manager must be fully functional. When Update Manager is present it is relied upon by NSX Manager to approve the install or uninstall or vibs. Resolve the issue with Update Manager, or uninstall Update Manager.
Once Update Manager is removed or repaired to a working state the service deployments will install successfully. This VMware KB confirms the issue occurs when Update Manager is unavailable and advises that modules are manually installed instead, however it is not clear in stating that the service deployments succeed without Update Manager, and therefore the UM instance can be removed as a work around.
esxsi.com 
I have this issue, except VUM is not installed and never has been, I’ve deployed this in 2 fresh test environments 6.0U2 and same problem, even if I install VUM the problem does not go away.
Any ideas?
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If it is a new vCenter and NSX Manager installation then it must be something left behind on the ESXi hosts, old vibs, pending reboot, or something else. You could try rebooting the hosts or SSH on to one and run ‘esxcli software vib list’, look for esx-vxlan and esx-vsip; if they are present then they’re left over from a previous NSX or guest introspection install. Try a vanilla build of ESXi if you’re able to rebuild. It’s a pretty common error so there’s quite a lot of things, troubleshooting KB may help https://kb.vmware.com/kb/2094261
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I had this error as well when I deployed NSX 6.4.4 into our vSphere/vCenter 6.0. I was able to resolved it by logging into our vCenter via vSphere web client > host and clusters > select the vCenter server > Manage > Settings > General > vCenter Server Settings > vCenter Server managed address > change the IP of the vCenter to the existing one.
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