rspec upgrade from 1.2.6 to 2.0.2 and/or 2.1.0

I am trying to upgrade a Rails 1.2.6 application to either 2.0.2 or
(preferably) 2.1.0 whichever works. The application has a hugh number
of rspec tests written. I am having problems getting past the first
base.
Details: The application has both rspec (1.1.3) and rspec_on_rails
plugins installed in vendor/plugins directory. The application also had
Rails 1.2.6 frozen in the vendor directory. When I ran the following
code snippet in the account_spec.rb file, it ran fine (with Rails 1.2.6
frozen in vendor directory).

require File.dirname(__FILE__) + '/../spec_helper'

describe Account do
  it "should have valid fixture defaults" do
    create_account.should be_valid
  end
end

"create_account" exists in the spec_helper.rb.

Now to upgrade, first in Rails 2.0.2. I removed the Rails directory
from vendor directory, changed rails version in environment.rb from
1.2.6 to 2.0.2 and tried to rerun the same file/test as above. The code
does not even get past the first line of code, i.e., require
File.dirname ....

I get the following exception trace:

/usr/local/lib/ruby/gems/1.8/gems/activesupport-2.0.2/lib/active_support/dependencies.rb:249:in
`load_missing_constant': Expected
/home/bruparel/work/isabont/app/models/employer.rb to define Employer
(LoadError)
        from
/usr/local/lib/ruby/gems/1.8/gems/activesupport-2.0.2/lib/active_support/dependencies.rb:453:in
`const_missing'
        from
/usr/local/lib/ruby/gems/1.8/gems/activesupport-2.0.2/lib/active_support/dependencies.rb:465:in
`const_missing'
        from
/usr/local/lib/ruby/gems/1.8/gems/activesupport-2.0.2/lib/active_support/dependencies.rb:471:in
`send'
        from
/usr/local/lib/ruby/gems/1.8/gems/activesupport-2.0.2/lib/active_support/dependencies.rb:471:in
`const_missing'

I am no rspec power user at this point, but have run rspec tests at
commmand line and in NetBeans IDE for Rails 1.2.x without any problems.
Thanks for your time.
Bharat

        from
/home/bruparel/work/isabont/vendor/plugins/fixture_replacement/lib/fixture_replacement/fixture_replacement_generator.rb:88:in
`const_get'
        from
/home/bruparel/work/isabont/vendor/plugins/fixture_replacement/lib/fixture_replacement/fixture_replacement_generator.rb:88:in
`add_to_class_singleton'
        from
/home/bruparel/work/isabont/vendor/plugins/fixture_replacement/lib/fixture_replacement/fixture_replacement_generator.rb:99:in
`assign_init_variables'
        from
/home/bruparel/work/isabont/vendor/plugins/fixture_replacement/lib/fixture_replacement/fixture_replacement_generator.rb:38:in
`initialize'
         ... 15 levels...
        from
/home/bruparel/work/isabont/vendor/plugins/rspec/lib/spec/runner/example_group_runner.rb:13:in
`load_files'
        from
/home/bruparel/work/isabont/vendor/plugins/rspec/lib/spec/runner/options.rb:85:in
`run_examples'
        from
/home/bruparel/work/isabont/vendor/plugins/rspec/lib/spec/runner/command_line.rb:19:in
`run'
        from /home/bruparel/work/isabont/vendor/plugins/rspec/bin/spec:4

The immediate problem has been solved with the help of someone who is
familiar with it.
The app used acts_as_list and acts_as_tree which was getting lost in the
stack trace. Since Rails 2.x has removed that from core, I had to
install them as plug-ins. It is working on Rails 2.0.2, next I will
attempt 2.1