Confused about D2 std.stdio

[Patrick Kreft]

I use normally writefln for output in console. Today i have read the 
announcement and test D2 and got that:

import std.stdio;

void main()
{
     //writeln("Hello"); // md\src\phobos\std\format.d(2087): template 
instance std.format.getNthInt!(invariant(char)[5u],char) error instantiating
     //writefln("Hello"); // tmd\src\phobos\std\format.d(2087): template 
instance std.format.getNthInt!(char) error instantiating
     write("Hello\n"); // <- work
     writef("Hello\n"); // <- work
}

Maybe somebody can explain me that?