The issue is not coming up in case of first time install, it is ocurring at the time of consecutive uninstall and install. In this scenario it looks like VMware is is cot cleaning up the previously registered webclient plugin.
Workaround: Restart the vsphere-ui i.e. the vsphere html ui service.
The impact of the work around is not much as we are only restarting the HTML UI and not the whole vcenter service. Moreover during the time of restart, Flex based UI will be accessible to the user.
This behavior is working fine for Flex while it is consistent HTL for vSpher 6.0 and 6.5 .
