Logon failure message while connectiong to SQL

Question

Hi all, I am developing an application using Sharepoint portal Server. The configuration for this is as fallows. IIS Directory Security : Integrated Windows Authentication [Note: No anonymous access here] SQL : Windows Authentication web.config : , When i try to access database under these configuration settings, i am getting an error stating as below "Login failed for user 'DOMAIN\UserName'.: at System.Data.SqlClient.ConnectionPool.GetConnection(Boolean& isInTransaction) at System.Data.SqlClient.SqlConnectionPoolManager.GetPooledConnection(SqlConnectionString options, Boolean& isInTransaction) at System.Data.SqlClient.SqlConnection.Open() at .... When i add the UserName under SQL Server Enterprise Manager -> Database -> Security -> New Login [Add that user here]. Then the SQL connection is working fine. I want to access database, without adding the User under Database->Security and keeping the configurations same. Can this be possible, if so what is the solution please let me know. Help is highly appreciated. Thanks in advance