I am receiving an "Invalid argument" error from File.utime.

irb> testfile = 'd:/temp/2007/06/test.txt'
=> "d:/temp/2007/06/test.txt"
irb> File.utime(0, Time.now, testfile)
Errno::EINVAL: Invalid argument - d:/temp/2007/06/test.txt
        from (irb):4:in `utime'
        from (irb):4
irb> File.exist?(testfile)
=> true
irb> File.writable?(testfile)
=> true

My local user group suggested:
irb> require 'time'
=> false

False?

I tried this on two computers:
| WinXP SP2 | WinXP SP2 |
| Ruby 1.8.6  | 1.8.5 |
| NTFS         | FAT32 |

A friend has these same specs, but it works for him.
Google for 'ruby, windows, File.utime, "Invalid Argument"' (and various versions
of this) doesn't help.  It does appear in a nice Ruby poetry jam.

Any ideas?