Rails 4.0.0.beta1 installation error

I am getting the following error while installing on windows with ruby v
2.0. I have installed DevKit for 64 bit.

Temporarily enhancing PATH to include DevKit…
Building native extensions. This could take a while…
ERROR: Error installing rails:
ERROR: Failed to build gem native extension.

d:/programs/Ruby200-x64/bin/ruby.exe extconf.rb

creating Makefile

generating atomic_reference-x64-mingw32.def
compiling atomic_reference.c
atomic_reference.c:1:0: error: CPU you selected does not support x86-64
ion set
make: *** [atomic_reference.o] Error 1

Gem files will remain installed in
ems/atomic-1.0.1 for inspection.
Results logged to

I get the same error, I solved with the 32bit version, ruby+devkit

Same error. Any ideas for workaround without switching to 32bit version
or Ruby? My CPU is indeed a x86-64 compatible CPU.