If you want help, then provide a more detailled problem description than just "Unable to Sign in.An error occurred during Authentication" including exact versions in use, current security setup etc.
Furthermore, you will need to be more precise about what you already tried, not just "I have looked at some blogs" since otherwise you'll get 50 suggestions which don't apply to you or you have already tried.
follow the link http://docs.oracle.com/cd/E21764_01/bi.1111/e10543/privileges.htm#BIESC721
And also try these steps
1.Take a backup of your webcatalog.
2.Navigate to \OBIEE11G\instances\instance2\bifoundation\OracleBIPresentationServicesComponent\coreapplication_obips1\catalog\SampleApp\root\users\Administrator\_prefs
3.Delete the files named "cacheduserinfo" and "cacheduserinfo.atr."
4.Open web browser and retest OBIEE 11g login for that user.