C:\>sqlplus / as sysdba
SQL*Plus: Release 11.2.0.1.0 Production on 星期四 1月 5 13:55:44 2012
Copyright (c) 1982, 2010, Oracle. All rights reserved.
ERROR:
ORA-28056: Writing audit records to Windows Event Log failed
ORA-28056: Writing audit records to Windows Event Log failed
如上错误的解决办法在metalink上面有四种不同的解决办法，我采用了其中的得一种，进入windows的时间管理器将相关日志清空后可以正常登陆。
metalink 原文如下:
Cause
The Event Viewer log is full and not able to log any more events.
Justified by unpublished Bug 6823281 ORA-28056 WRITING AUDIT RECORDS TO WINDOWS EVENT LOG FAILED
which was closed as not a bug.
Solution
Try doing the following using Windows Event Viewer:
To open Event Viewer, click Start, click Control Panel,
click Performance and Maintenance, click Administrative Tools,
and then double-click Event Viewer.
You must be logged on as an administrator or a member of the
Administrators group to free an event log.
1) When a log is full, it stops recording new events. Clearing the log
is one way to free the log and start recording new events.
2) You can also free a log and start recording new events by overwriting
old events. To overwrite events, on the Action menu, click Properties,
and then click Overwrite events as needed. This ensures that all new
events are written to the log, even when the log is full.
3) You can also start logging new events by increasing the maximum
log size. To increase the log size, on the Action menu, click Properties,
and then increase the Maximum log size.
References