创建DBLink后，提示ora-12560 TNS 协议适配器错误

按以下语句创建dblink
create public database link TEST5
  connect to B
  identified by b
  using '(DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.240)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVICE_NAME = orcl)
    )
  )';创建成功后进行测试，测试语句是：select * from dual@TEST5提示“ora-12560 TNS  协议适配器错误”
不知道什么原因，有没有哪位高手知道的，给指点下？