NameError: undefined method `tables' for class `ActiveRecord::ConnectionAdapters::PostgreSQLAdapter'

I have an old 3.1 app I'm working on

I get this error when I run "rake db:schema:dump"...

"NameError: undefined method `tables' for class `ActiveRecord::ConnectionAdapters::PostgreSQLAdapter'"

I am stumped by this and I'm not sure where to start looking for a solution. The almighty google is coming up short. Any suggestions greatly appreciated.