处于restricted模式下？
数据库受限模式，在这个模式下只有RESTRICTED SESSION 权限的人才可以登陆，一般用与数据库维护的时候使用。
RESTRICTED SESSION Clause The RESTRICTED SESSION clause lets you restrict logon to Oracle. You can use this clause regardless of whether your instance has the database dismounted or mounted, open or closed. Restricting Session Logons: Example You may want to restrict logons if you are performing application maintenance and you want only application developers with RESTRICTED SESSION system privilege to log on. To restrict logons, issue the following statement: ALTER SYSTEM
