Safari generate a 500 internal server error on ajax requests

I have a shared hosting with hostgator.com. it use rails 2.2.2, cgi+mongrel When i try to do an ajax request with safari, i receive this error:

/!\ FAILSAFE /!\ Sat Jan 03 05:00:10 -0600 2009
Status: 500 Internal Server Error
can't modify frozen string

/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/request.rb:598:in `gsub!'
/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/request.rb:598:in `clean_up_ajax_request_body!'
/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/request.rb:508:in `parse_formatted_request_parameters'
/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/request.rb:441:in `request_parameters'                
/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/request.rb:392:in `parameters'                        
/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/request.rb:30:in `_unmemoized_request_method'         
/usr/lib/ruby/gems/1.8/gems/activesupport-2.2.2/lib/active_support/memoizable.rb:57:in `request_method'                  
/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/request.rb:40:in `method'                             
/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/routing/route_set.rb:433:in `extract_request_environment'
/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/routing/route_set.rb:386:in `recognize'                  
/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/dispatcher.rb:182:in `handle_request'                    
/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/dispatcher.rb:110:in `dispatch_unlocked'                 
/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/dispatcher.rb:123:in `dispatch'                          
/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/dispatcher.rb:122:in `synchronize'                       
/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/dispatcher.rb:122:in `dispatch'                          
/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/dispatcher.rb:132:in `dispatch_cgi'                      
/usr/lib/ruby/gems/1.8/gems/actionpack-2.2.2/lib/action_controller/dispatcher.rb:39:in `dispatch'                           
dispatch.cgi:10                                                                                                             

Thanks