I have created a new Ruby Project containing just the following line of code:

puts $LOAD_PATH

Here the result:
C:/xxxxx/Prototype/RubyApplication4/lib-IC:/xxxxx/Prototype/RubyApplication4/test
C:/xxxxx/Prototype/RubyApplication4/spec
C:/Program Files/Netbeans 6.9/ruby/jruby-1.5.0/lib/ruby/site_ruby/1.8
C:/Program Files/Netbeans 6.9/ruby/jruby-1.5.0/lib/ruby/site_ruby/shared
C:/Program Files/Netbeans 6.9/ruby/jruby-1.5.0/lib/ruby/1.8
.

as seen above the load path to the "lib" and the "test" directory got connected by a "-I" ans thus became invalid. 

As workaround I have figured out the following solutions:
In the test_suite file add the path to the test directory by adding the line:
$:.unshift File.join(File.dirname(__FILE__),'..','test')

Example:
------------- begin --------------
require 'test/unit'

require File.join(File.dirname(__FILE__),'..','test', 'test_lib' )

# Workaround for Netbeans 6.9 LOAD_PATH problem
$:.unshift File.join(File.dirname(__FILE__),'..','test')

# Add your testcases here
require 'tc_1'
require 'tc_2'
--------------- end ---------------
In each file accessing the lib directory from the test directory, add the line:
$:.unshift File.join(File.dirname(__FILE__),'..','lib')


Example:
------------- begin --------------
$:.unshift File.join(File.dirname(__FILE__),'..','lib')

require 'test/unit'

# For each file to be loaded from lib directory:
require File.join(File.dirname(__FILE__),'..','lib', 'xyz_node' )

class Tc_1 < Test::Unit::TestCase

  def setup
    # started before executing each test case
    puts("------------------------------------------------------------------")
  end


  def test_dump_database_node()
    create_node = XYZ_node.new()
  end
end
--------------- end ---------------

Please fix the loadpath.


Maybe the invalid load path is caused by this line:
rake aborted!
Command failed with status (1): [C:/jruby-1.5.1/bin/jruby.bat -I"lib" -r"C:...]
rake aborted!


Note:
Same error appears with build-in jruby and external jruby.