airminer

The problem is probably that the directory you keep ksp in is write-protected. Turn that off. (I use Steam, and when I turned write protection off on the \steamapps\Kerbal Space Program folder this message disappeared)

So, Squad has removed the ban on the System.IO namespace with 0.21. Will you merge the plugin and the client?

You can check what plugins are loaded in the debug menu, under the tab named "assemblies".