Connecting to SQL Server from Windows Vista – Error 18456

When you try to connect to SQL Server from Windows Vista using Windows authentication you may get the following error:

Login failed for user 'Server_name\Login_name'. (Microsoft SQL Server, Error: 18456)

Windows Vista User Account Control (UAC) security feature lets users perform tasks as non-Administrators, and to start a program with administrator permissions, user needs to provide consent. On Windows Vista, when a user tries to connect to SQL Server, a message may be returned that the account does not have rights to log in to SQL Server.

To run SQL Server Management Studio as administrator:
Right-click SQL Server Management Studio from Programs list, and then click 'Run as administrator' to elevate the user permissions:

For more information about other Error messages 18456, 18488 and 18470 read previous blog post:
Login failed error messages in SQL Server – Errors 18456, 18488 and 18470