Error in saving contents

i am able to login to drupal as admin but when ever i try 开发者_JS百科to save any content or settings i get the error

The username admin does not exist

This is probably due to a user related module altering the $user object. Your first and best bet is to make sure you are fully up to date with all your modules. If that doesn't solve it, you should disable modules one at a time until this error goes away. Any modules related to profiles or users should be suspect - content profile, etc.