--as sysdba 是不能省略的。
C:\Documents and Settings\Administrator>sqlplus sys/oracle as sysdba

SQL*Plus: Release 10.2.0.1.0 - Production on 星期四 8月 11 15:43:03 2011

Copyright (c) 1982, 2005, Oracle.  All rights reserved.


连接到:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
[SYS@myorcl] SQL>exit
从 Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options 断开

C:\Documents and Settings\Administrator>sqlplus scott/tiger

SQL*Plus: Release 10.2.0.1.0 - Production on 星期四 8月 11 15:43:14 2011

Copyright (c) 1982, 2005, Oracle.  All rights reserved.


连接到:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options

[SCOTT@myorcl] SQL>

------解决方案--------------------
一楼正解，as sysdba

------解决方案--------------------
对。/as sysdba   如果还是报错，你得检查oracle软件里面的dll

------解决方案--------------------
as sysdba…