drupal webservice error Access denied for user anonymous experts:

I am new to drupal webservice,when I have set up the backend drupal webservice,I am trying
to use firefox poster plugin to test the user/login function but I always get "Access denied for user anonymous" message ,after what I have check and searched the solution all around internet I can't find out why this error happen,could anyone who kindly take a look and help me?thank you so much in advance.

1 using firefox poster to post message and get response like below snapshot:


2 after checked the http message in fiddler,I still confused that every thing seems correct 
but still error message for "Access denied for user anonymous"


3 here is my webservice configration:
This most likely has to do with permissions for anonymous user. Try updating permissions and it should solve your issue.