parallel.log

(in /var/www/vhosts/app.com/httpdocs/releases/20110908191805)
** Invoke item_statistics:update (first_time)
** Invoke environment (first_time)
** Execute environment
** Execute item_statistics:update
rake aborted!
private method `chomp' called for nil:NilClass
/opt/ree/lib/ruby/gems/1.8/gems/parallel-0.5.8/lib/parallel.rb:144:in `work_in_processes'
/opt/ree/lib/ruby/gems/1.8/gems/parallel-0.5.8/lib/parallel.rb:211:in `join'
/opt/ree/lib/ruby/gems/1.8/gems/parallel-0.5.8/lib/parallel.rb:211:in `wait_for_threads'
/opt/ree/lib/ruby/gems/1.8/gems/parallel-0.5.8/lib/parallel.rb:209:in `each'
/opt/ree/lib/ruby/gems/1.8/gems/parallel-0.5.8/lib/parallel.rb:209:in `wait_for_threads'
/opt/ree/lib/ruby/gems/1.8/gems/parallel-0.5.8/lib/parallel.rb:20:in `in_threads'
/opt/ree/lib/ruby/gems/1.8/gems/parallel-0.5.8/lib/parallel.rb:132:in `work_in_processes'
/opt/ree/lib/ruby/gems/1.8/gems/parallel-0.5.8/lib/parallel.rb:57:in `map'
/opt/ree/lib/ruby/gems/1.8/gems/parallel-0.5.8/lib/parallel.rb:32:in `each'
/var/www/vhosts/app.com/httpdocs/releases/20110908191805/lib/tasks/item_statistics.rake:9
/opt/ree/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/batches.rb:58:in `find_in_batches'
/opt/ree/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/base.rb:2148:in `with_scope'
/opt/ree/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/batches.rb:54:in `find_in_batches'
/opt/ree/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/named_scope.rb:186:in `send'
/opt/ree/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/named_scope.rb:186:in `method_missing'
/opt/ree/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/base.rb:2148:in `with_scope'
(__DELEGATION__):2:in `__send__'
(__DELEGATION__):2:in `with_scope'
/opt/ree/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/named_scope.rb:179:in `method_missing'
/var/www/vhosts/app.com/httpdocs/releases/20110908191805/lib/tasks/item_statistics.rake:8
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `call'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `execute'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `each'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `execute'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:597:in `invoke_with_call_chain'
/opt/ree/lib/ruby/1.8/monitor.rb:242:in `synchronize'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:583:in `invoke'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2051:in `invoke_task'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `top_level'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `each'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `top_level'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2023:in `top_level'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2001:in `run'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:1998:in `run'
/opt/ree/lib/ruby/gems/1.8/gems/rake-0.8.7/bin/rake:31
/opt/ree/bin/rake:19:in `load'
/opt/ree/bin/rake:19

looks like the process responds to gets without data, which could happen if it dies in a strange way, but my guess would be that centos maybe handles stuff differently...
can you try to replace line 144 with:

      until read = worker[:read].gets; end
      output = decode(read)

and run again on the production system