Cattr_accessor not found for testing?

Hi,

I have installed rails 2.0.2 on Linux (Fedora).

Everything works fine. but i have this problem when perform: rake
test:units

i get this error:
undefined method `cattr_accessor’ for FileMonitor:Class (NoMethodError)

even this class works fine in the real application, i still get this
error!!

I tried to re-install rails but still the same problem happens.
I searched in the internet and found some one suggesting: export
RUBYOPT=-rubygems
I tried it but still it is not working.

any help is appreciated,
Mohammad