Error: module ctype is in file 'std/ctype.d' which cannot be read - when running dmd

[Roman via Digitalmars-d-learn]

I should probably add that only importing std.ctype causes the 
error.
I have a bunch of other imports:

     import std.stdio, std.string, std.algorithm, std.conv, 
std.ctype, std.regex, std.range;

If I remove std.ctype, it compiles just fine.