Rails - Apr 2005 - NoMethodError (undefined method `fetch_fields' for nil:NilClass)

Hi

I''m new to Rails (and Ruby) and I can''t get it to work
properly.
Every time I want to do something with my database-connection (e.g.  
use scaffold) I get this, or something similiar (from development.log):


 >> Beneath this code there''s some more text <<

-------

Processing CategoryController#index (for 127.0.0.1 at Tue Apr 26  
21:43:45 CEST 2005)
   Parameters: {"action"=>"index",
"controller"=>"category"}
   [4;33mCategory Count (0.001415)   [1;37mSELECT COUNT(*) FROM  
categories 


NoMethodError (undefined method `fetch_fields'' for nil:NilClass):
     /usr/lib/ruby/gems/1.8/gems/activerecord-1.10.1/lib/ 
active_record/connection_adapters/mysql_adapter.rb:204:in `select''
     /usr/lib/ruby/gems/1.8/gems/activerecord-1.10.1/lib/ 
active_record/connection_adapters/mysql_adapter.rb:98:in `select_one''
     /usr/lib/ruby/gems/1.8/gems/activerecord-1.10.1/lib/ 
active_record/base.rb:452:in `count_by_sql''
     /usr/lib/ruby/gems/1.8/gems/activerecord-1.10.1/lib/ 
active_record/base.rb:445:in `count''
     /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/pagination.rb:154:in
`count_collection_for_pagination''
     /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/pagination.rb:171:in `paginator_and_collection_for''
     /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/pagination.rb:111:in `paginate''
     /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/scaffolding.rb:101:in `list''
     /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/scaffolding.rb:94:in `index''
     /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/base.rb:708:in `send''
     /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/base.rb:708:in `perform_action_without_filters''
     /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/filters.rb:294:in `perform_action_without_benchmark''
     /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/benchmarking.rb:37:in `perform_action_without_rescue''
     /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/benchmarking.rb:37:in `measure''
     /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/benchmarking.rb:37:in `perform_action_without_rescue''
     /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/rescue.rb:79:in `perform_action''
     /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/base.rb:330:in `send''
     /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/base.rb:330:in `process''
     /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/base.rb:273:in `process''
     /usr/lib/ruby/gems/1.8/gems/rails-0.12.1/lib/dispatcher.rb:32:in  
`dispatch''
     /Volumes/Documents/home/WebServer/Documents/ToDo/public/ 
dispatch.cgi:10


Rendering /usr/lib/ruby/gems/1.8/gems/actionpack-1.8.1/lib/ 
action_controller/templates/rescues/layout.rhtml (500 Internal Error)

-------

In the browser the page only displays some error message stuff like  
"NoMethodError (undefined method `fetch_fields'' for
nil:NilClass):".

I followed some tutorials and I always got something like this when  
using scaffold, so it must be my setup. I use Mac OS X. Any help is  
much appreciated!

Kind regards,
Marc