今天在安装11g（11.1.0.7.0）之后，通过emca -config dbcontrol db -repos create 命令手工创建em的时候报错，查看日志后发现有以下错误：
CONFIG: Spooling to C:\app\Administrator\cfgtoollogs\emca\orcl\emca_repos_create_2009_01_16_06_44_13.log
Jan 16, 2009 6:44:13 AM .sysman.emcp.EMReposConfig createRepository
INFO: Creating the EM repository (this may take a while) ...
Jan 16, 2009 6:44:13 AM oracle.sysman.emcp.EMReposConfig createRepository
CONFIG: ORA-20001: SYSMAN already exists..
ORA-06512: at line 17
oracle.sysman.assistants.util.sqlEngine.SQLFatalErrorException: ORA-20001: SYSMAN already exists..
ORA-06512: at line 17
at oracle.sysman.assistants.util.sqlEngine.SQLEngine.executeImpl(SQLEngine.java:1530)
at oracle.sysman.assistants.util.sqlEngine.SQLEngine.executeScript(SQLEngine.java:880)
at oracle.sysman.assistants.util.sqlEngine.SQLPlusEngine.executeScript(SQLPlusEngine.java:270)
at oracle.sysman.assistants.util.sqlEngine.SQLPlusEngine.executeScript(SQLPlusEngine.java:311)
at oracle.sysman.emcp.EMReposConfig.createRepository(EMReposConfig.java:492)
at oracle.sysman.emcp.EMReposConfig.invoke(EMReposConfig.java:218)
at oracle.sysman.emcp.EMReposConfig.invoke(EMReposConfig.java:147)
at oracle.sysman.emcp.EMConfig.perform(EMConfig.java:222)
at oracle.sysman.emcp.EMConfigAssistant.invokeEMCA(EMConfigAssistant.java:535)
at oracle.sysman.emcp.EMConfigAssistant.performConfiguration(EMConfigAssistant.java:1215)
at oracle.sysman.emcp.EMConfigAssistant.statusMain(EMConfigAssistant.java:519)
at oracle.sysman.emcp.EMConfigAssistant.main(EMConfigAssistant.java:468)
Jan 16, 2009 6:44:13 AM oracle.sysman.emcp.EMReposConfig invoke
SEVERE: Error creating the repository
Jan 16, 2009 6:44:13 AM oracle.sysman.emcp.EMReposConfig invoke
INFO: Refer to the log file at C:\app\Administrator\cfgtoollogs\emca\orcl\emca_repos_create_
Jan 16, 2009 6:44:13 AM oracle.sysman.emcp.EMConfig perform
SEVERE: Error creating the repository
Refer to the log file at C:\app\Administrator\cfgtoollogs\emca\orcl\emca_2009_01_16_06_43_53.log for more details.
Jan 16, 2009 6:44:13 AM oracle.sysman.emcp.EMConfig perform
CONFIG: Stack Trace:
oracle.sysman.emcp.exception.EMConfigException: Error creating the repository
at oracle.sysman.emcp.EMReposConfig.invoke(EMReposConfig.java:230)
at oracle.sysman.emcp.EMReposConfig.invoke(EMReposConfig.java:147)
at oracle.sysman.emcp.EMConfig.perform(EMConfig.java:222)
at oracle.sysman.emcp.EMConfigAssistant.invokeEMCA(EMConfigAssistant.java:535)
at oracle.sysman.emcp.EMConfigAssistant.performConfiguration(EMConfigAssistant.java:1215)
at oracle.sysman.emcp.EMConfigAssistant.statusMain(EMConfigAssistant.java:519)
at oracle.sysman.emcp.EMConfigAssistant.main(EMConfigAssistant.java:468)
经过同事提醒，才知道自己犯了一个很白痴的错误，在手工创建EM之前，需要先要删除EM配置信息：
具体操作如下：
1、使用emca -deconfig dbcontrol db命令删除配置
2、使用emca -repos drop删除repository
3、使用emca -config dbcontrol db -repos create 创建Database Control。
以上操作，也适用于，小记下，O(∩_∩)O哈哈~，下次一定不能犯同样的错误