In some cases, permissions on the vCenter can prevent the VMan console from removing a plugin after it has been added.
Do the following steps to manually remove an unnecessary plugin from VMWare:
1. On the web browser, navigate to http://vCenter_Server_name_or_IP/mob.
Where, vCenter_Server_name_or_IP/mob is the name of the vCenter Server or its IP address.
2. Click Content.
3. Click Extension Manager.
4. Select and copy the name of the plugin to be removed from the list of values under Properties.
5. In the new window that will appear, paste the name of the plugin and click Invoke Method. This will remove the plugin.
VMan Plugin Name: extensionList["com.hyper9.plugin.flex"]
6. Close the window.
7. Refresh the Managed Object Type:ManagedObjectReference:ExtensionManager window to verify that the plugin was successfully removed.
For more information, please refer to the Removing unwanted plugins from vCenter Server (1025369) document.