Yes, @Digitizer is correct. Negative Lab Pro will not work currently from within that folder because of folder permission issues with Windows.
You need to:
- Close Lightroom
- Move the plugin from C:\Program Files\Adobe\Common\Plugin-ins\NegativeLablPro.lrplugin to a folder you create on the root drive, for instance, C:\Plugins
- Re-open Lightroom.
- Go to File > Plugin Manager
- Click “remove” to remove the previous location of Negative Lab Pro, then click “add” and navigate to “C:\Plugins” to add the plugin you just moved to there.
-Nate