Gem compilation failing on AIX 64 bit box

I’m trying to compile ruby 64 bit on aix 64 bit box.
I configured ruby by enabling libpthread. and compiled the same.
But when i try to run ruby setup.rb, i get the following error:

/home/xyz/RUBY_64/lib/ruby/1.8/ load failed -
/home/xyz/RUBY_64/lib/ruby/1.8/ (LoadError)
from /home/xyz/RUBY_64/lib/ruby/1.8/thread.rb:5
from /home/xyz/RUBY_64/lib/ruby/site_ruby/1.8/rubygems.rb:85:in
require' from /home/xyz/RUBY_64/lib/ruby/site_ruby/1.8/rubygems.rb:85 from /home/xyz/RubyAndRelatedGems/7.3/rubygems-0.9.4/./post-install.rb:81:inrequire’
install_sources' from /home/xyz/RubyAndRelatedGems/7.3/rubygems-0.9.4/./post-install.rb:116:inrun_hook’
from setup.rb:1526:in exec_task_traverse' from setup.rb:1342:inexec_install’
from setup.rb:1000:in exec_install' from setup.rb:814:ininvoke’
from setup.rb:773:in `invoke’
from setup.rb:1578

I’ve tried the same with ruby -d option and it does not give any more
Also, ldd on does not show any dependencies!

any idea?