Logon Error: 18487, Severity: 14, State: 1. Logon Login failed for user 'loginname'. Reason: The password of the account has expired. [CLIENT:
Then the password for the login used in your web application has expired. SQL Server 2005 introduced 'Enforce password policy' and/or the 'Enforce password expiration' configurations which use the local policies for password length, complexity and expiration. Depending on how Active Directory, the local policies and your rights are setup, these parameters can be reviewed and changed to dictate how SQL Server uses configurations.