using jquery ajax with codeigniter

[eluser]fatfishy[/eluser]
yes, ive changed the $.ajax() data: variable too!

Code:

$.ajax({
  type: "POST",
  url: "http://127.0.0.1/index.php/ajax/username_taken",
  data: { username:username },
  success: function(msg) {
  alert("asD");
   $("#status").html(msg);
  }
});

and here is the ss - http://s12.postimage.org/o3c5xnuj1/error.jpg

[quote author="Mirge" date="1352991465"]Check your error log to see why it's throwing a 500 error.[/quote]
I tried now to turn on the logs and see what is says but I don't see something about it,

DEBUG - 2012-11-15 16:48:38 --> Config Class Initialized
DEBUG - 2012-11-15 16:48:38 --> Hooks Class Initialized
DEBUG - 2012-11-15 16:48:38 --> Utf8 Class Initialized
DEBUG - 2012-11-15 16:48:38 --> UTF-8 Support Enabled
DEBUG - 2012-11-15 16:48:38 --> URI Class Initialized
DEBUG - 2012-11-15 16:48:38 --> Router Class Initialized
DEBUG - 2012-11-15 16:48:38 --> No URI present. Default controller set.
DEBUG - 2012-11-15 16:48:38 --> Output Class Initialized
DEBUG - 2012-11-15 16:48:38 --> Security Class Initialized
DEBUG - 2012-11-15 16:48:38 --> Input Class Initialized
DEBUG - 2012-11-15 16:48:38 --> XSS Filtering completed
DEBUG - 2012-11-15 16:48:38 --> XSS Filtering completed
DEBUG - 2012-11-15 16:48:38 --> XSS Filtering completed
DEBUG - 2012-11-15 16:48:38 --> CRSF cookie Set
DEBUG - 2012-11-15 16:48:38 --> Global POST and COOKIE data sanitized
DEBUG - 2012-11-15 16:48:38 --> Language Class Initialized
DEBUG - 2012-11-15 16:48:38 --> Loader Class Initialized
DEBUG - 2012-11-15 16:48:38 --> Database Driver Class Initialized
DEBUG - 2012-11-15 16:48:38 --> Controller Class Initialized
DEBUG - 2012-11-15 16:48:38 --> Helper loaded: form_helper
DEBUG - 2012-11-15 16:48:38 --> Form Validation Class Initialized
DEBUG - 2012-11-15 16:48:38 --> File loaded: application/views/test.php
DEBUG - 2012-11-15 16:48:38 --> Final output sent to browser
DEBUG - 2012-11-15 16:48:38 --> Total execution time: 0.1645
DEBUG - 2012-11-15 16:48:40 --> Config Class Initialized
DEBUG - 2012-11-15 16:48:40 --> Hooks Class Initialized
DEBUG - 2012-11-15 16:48:40 --> Utf8 Class Initialized
DEBUG - 2012-11-15 16:48:40 --> UTF-8 Support Enabled
DEBUG - 2012-11-15 16:48:40 --> URI Class Initialized
DEBUG - 2012-11-15 16:48:41 --> Router Class Initialized
DEBUG - 2012-11-15 16:48:41 --> Output Class Initialized
DEBUG - 2012-11-15 16:48:41 --> Security Class Initialized
DEBUG - 2012-11-15 16:48:41 --> Input Class Initialized
DEBUG - 2012-11-15 16:48:41 --> XSS Filtering completed
DEBUG - 2012-11-15 16:48:41 --> XSS Filtering completed
DEBUG - 2012-11-15 16:48:41 --> XSS Filtering completed
DEBUG - 2012-11-15 16:48:41 --> XSS Filtering completed

thanks!