if you'r using the File and you get that error try using the full name (with namespaces too)
so instead of (for example)
File file = new File()
use
System.IO.File file = new System.IO.File()
that's the better way.
otherwise you can use alias for namespaces,
using siof= System.IO.File;
using sf= Scripting.File
....
siof.File file = new siof.File()
sf.File file = new sf.File()