Undefined method `as' for #<Arel::Table

[stpi...@hotmail.com]

when i go to to the localhost and i create a new page
its give this error and i could not fix this error mesagge

undefined method `as' for #<Arel::Table:0x7e30f1b4>

Rails.root: /home/jonathanandrades/jonathan/adva_app

Application Trace | Framework Trace | Full Trace

simple_nested_set (0.0.28) lib/simple_nested_set/nested_set.rb:137:in
denormalize_level_query' simple_nested_set (0.0.28) lib/
simple_nested_set/nested_set.rb:60:indenormalize!'
simple_nested_set (0.0.28) lib/simple_nested_set/nested_set.rb:48:in
save!' simple_nested_set (0.0.28) lib/simple_nested_set/act_macro.rb:
16:in_callback_after_342'
activesupport (3.0.3) lib/active_support/callbacks.rb:430:in
_run_save_callbacks' activerecord (3.0.3) lib/active_record/
callbacks.rb:277:increate_or_update'
activerecord (3.0.3) lib/active_record/persistence.rb:39:in save'
activerecord (3.0.3) lib/active_record/validations.rb:43:insave'
activerecord (3.0.3) lib/active_record/attribute_methods/dirty.rb:
21:in save' activerecord (3.0.3) lib/active_record/transactions.rb:
237:insave'
activerecord (3.0.3) lib/active_record/transactions.rb:289:in
with_transaction_returning_status' activerecord (3.0.3) lib/
active_record/connection_adapters/abstract/database_statements.rb:
139:intransaction'
activerecord (3.0.3) lib/active_record/transactions.rb:204:in
`transaction'