ml-build broken in windows?

I'm using SMLNJ 110.59 in Cygwin (atop WinXP) and I can't build heaps 
with ml-build. Here's my simplest example:

foo.sml:

     structure Foo = struct
     fun main() = TextIO.print "hello, world!\n"
     end

foo.cm:

     Library
             structure Foo
     is
             foo.sml
             $/basis.cm
             $/smlnj-lib.cm

At the shell I had the following interaction:

     % ml-build foo.cm Foo.main foo.heap
     Standard ML of New Jersey v110.59 [built: Mon Nov  6 09:23:07 2006]
     [scanning foo.cm]
     /c/smlnj/bin/sml: Fatal error -- Uncaught exception Io with 
<unknown> raised at
     Basis/Implementation/IO/bin-io-fn.sml:618.24-618.71

This is a cryptic error (I'm not sure where to find bin-io-fn.sml...?), 
but according to Google it appears to be a "file not found." What file 
is missing, I couldn't say.

Is ml-build known not to work in Windows? Can someone help me figure out 
what's going wrong?

Much obliged,
Dave

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