From the error it sounds like you have a script in your project that defines Path in the global namespace, conflicting with System.IO.Path. Scripts should always use a namespace to avoid conflicts. Search your project for Path scripts. Start by searching the Project view for Path since scripts are often called the same as class names. If you find the script, you can delete it if you're not using it, or notify the author of the conflict. Either way, let us know what you find!