Hi, This snippet seems to be a bug in IronRuby. file = Kernel.open("test.bin", "wb", 0444) Error: wrong number of arguments (5 for 3) (ArgumentError) which due to KernelOps.cs - open method doesn''t have overload to take a permission parameter. Open bug at - http://rubyforge.org/tracker/index.php?func=detail&aid=25308&group_id=4359&atid=16798 Thank you, -Jirapong