Make sure that .prm file is not used by some other app. For example, you might have Preimere Pro running that has this plugin loaded and, when you try to rebuild the plugin, VS probably has to delete old .prm file and write new one. Well, it can't, since it is in use.
You have to set an Environment variable called PREMSDKBUILDPATH:
On Windows, to specify where you want the built plug-ins to go, set a user environment variable (right-click My Computer > Properties > Advanced > Environment Variables > User variables) called PREMSDKBUILDPATH to the desired path (e.g. "C:\Program Files\Adobe\Common\Plug-ins\CSXX\MediaCore"), and re-log in so that the variable will be set. In the Visual Studio Property Pages for each SDK project, this path is the base path for the Output Directory.