Thanks to Driven and Dan.
I will use new notation instead use force_encoding. I think now it should works...
#UUID in RUBY 2.0 WINDOWS
` cmd="wmic csproduct get uuid"
filename = File.join(ENV["TMP"],"backquote.out")
exec_string = "`" + cmd + " > " + filename + "`"
exec_string.gsub! '\\', '/'
eval("#{exec_string}")
uuid=""
open(filename, "r:BOM|utf-16le:UTF-8") do |io|
uuid = io.read
end`