Some questions about rake

well , rake , I use rake 0.8.1 , rails 2.1 , db2 9.5, trying to
migrate,but get this error ,why?

rake db:migrate --trace
(in D:/ruby/work/depots)
rake db:migrate
** Invoke db:migrate (first_time)
** Invoke environment (first_time)
** Execute environment
** Execute db:migrate
rake aborted!
select_rows is an abstract method
d:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/
connection_adapters/abstract/database_statements.rb:34:in
`select_rows'
d:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/
connection_adapters/abstract/database_statements.rb:27:in
`select_values'
d:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/
migration.rb:373:in `current_version'
d:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/
migration.rb:392:in `current_version'
d:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/
migration.rb:406:in `migrate'
d:/ruby/lib/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
inflector.rb:283:in `detect'
d:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/
migration.rb:406:in `each'
d:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/
migration.rb:406:in `detect'
d:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/
migration.rb:406:in `migrate'
d:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/
migration.rb:357:in `up'
d:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/
migration.rb:340:in `migrate'
d:/ruby/lib/ruby/gems/1.8/gems/rails-2.1.0/lib/tasks/databases.rake:99
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:546:in `call'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:546:in `execute'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:541:in `each'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:541:in `execute'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:508:in
`invoke_with_call_chain'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:501:in
`synchronize'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:501:in
`invoke_with_call_chain'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:494:in `invoke'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:1931:in
`invoke_task'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:1909:in
`top_level'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:1909:in `each'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:1909:in
`top_level'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:1948:in
`standard_exception_handling'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:1903:in
`top_level'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:1881:in `run'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:1948:in
`standard_exception_handling'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake.rb:1878:in `run'
d:/ruby/lib/ruby/gems/1.8/gems/rake-0.8.1/bin/rake:31
d:/ruby/bin/rake:16:in `load'
d:/ruby/bin/rake:16