Permission error in "ri" command

Hi - I get the following error when I run “ri” command.
I’m using Mac OS X Snow Leopard. I installed Ruby with MacPorts.

/opt/local/lib/ruby/gems/1.8/gems/rdoc-2.3.0/lib/rdoc/ri/driver.rb:405:in
initialize': Permission denied - /Users/jon/.ri/cache/.doc_dirs (Errno::EACCES) from /opt/local/lib/ruby/gems/1.8/gems/rdoc-2.3.0/lib/rdoc/ri/driver.rb:405:inopen’
from
/opt/local/lib/ruby/gems/1.8/gems/rdoc-2.3.0/lib/rdoc/ri/driver.rb:405:in
create_class_cache' from /opt/local/lib/ruby/gems/1.8/gems/rdoc-2.3.0/lib/rdoc/ri/driver.rb:389:inclass_cache’
from
/opt/local/lib/ruby/gems/1.8/gems/rdoc-2.3.0/lib/rdoc/ri/driver.rb:474:in
display_name' from /opt/local/lib/ruby/gems/1.8/gems/rdoc-2.3.0/lib/rdoc/ri/driver.rb:787:inrun’
from
/opt/local/lib/ruby/gems/1.8/gems/rdoc-2.3.0/lib/rdoc/ri/driver.rb:786:in
each' from /opt/local/lib/ruby/gems/1.8/gems/rdoc-2.3.0/lib/rdoc/ri/driver.rb:786:inrun’
from
/opt/local/lib/ruby/gems/1.8/gems/rdoc-2.3.0/lib/rdoc/ri/driver.rb:315:in
run' from /opt/local/lib/ruby/gems/1.8/gems/rdoc-2.3.0/bin/ri:5 from /opt/local/bin/ri:19:inload’
from /opt/local/bin/ri:19

Can anybody help solve this issue?

-jon

First things first: does the file exist?
/Users/jon/.ri/cache/.doc_dirs