Reason for the error : Windows Vista users that are members of the Windows Administrators group are not automatically granted permission to connect to SQL Server, and they are not automatically granted administrative privileges.
Resolution: Grant rights to the administrator. Follow these steps:
Step 1: Go to Start > All Programs > Microsoft SQL Server 2005 > Configuration Tools > SQL Server Surface Area Configuration.
Step 2: Click on 'Add New Administrator'.
Step 3: In the 'SQL Server User Provisioning on Vista' dialog box, look out for the 'Member of the SqlServer SysAdmin role ' in the 'Available Privileges' box. Transfer it to the 'Privileges that will be granted to' box. Click Ok.
Note: You will be able to see 'Add New Administrator' in the Configuration tool only if you have logged in as an administrator