Web server won't start after freezing gems

My hosting company recently upgraded their Rails version, so I want to
freeze my app to Rails version 1.2.3. I was able to freeze it
successfully, but when I try to start the server on my local
development environment, I’m confronted with this error:

./script/…/config/…/vendor/rails/railties/lib/initializer.rb:43:in
send': undefined methodinstall_gem_spec_stubs’ for
#Rails::Initializer:0x290444c (NoMethodError)
from ./script/…/config/…/vendor/rails/railties/lib/initializer.rb:
43:in run' from ./script/../config/boot.rb:46:inload_initializer’
from ./script/…/config/boot.rb:38:in run' from ./script/../config/boot.rb:11:inboot!’
from ./script/…/config/boot.rb:109
from ./script/server:2:in require' from ./script/server:2 from -e:4:inload’
from -e:4

Does anyone know what I can do to resolve this? Thanks.