Resetting WebLogic admin password

I have faced an issue in reseting weblogic admin user password. Following are the steps i have executed in sequence.please help to understand why it is not working this way

I have 2 managed instances running on two separate computers.

Step 1. shutdown the admin server instance ( i did not shutdown the node manager and other 2 manage server instances

Step 2. Set the environment variables

cd $DOMAIN_HOME/bin

. ./setDomainEnv.sh

Step 3. then executed the command below to create the new password

cd ../security
mv DefaultAuthenticatorInit.ldift oldDefaultAuthenticator
java weblogic.security.utils.AdminAccount weblogic new_password . 

Step 4. backed up existing boot.properties file and created a new file. Also backed up data directory of admin server. created a new boot.properties file with following configuration

with plain text username(weblogic_admin) and password (new_password).

cd ../servers/AdminServer
mv data data_old
cd security/
mv boot.properties oldboot.properties 

Step 5. Then i restarted the admin server. admin server is restarted successfully and i was able to login the admin console with my new username and password. Issue came when i try to shoutdown the admin server. when i execute sh stopWeblogicAdmin.sh , it will through following exception. But , if i kill the admin server process , then i am able to start the admin server with out any problem. and i am able to login to the server also. I am also able to stop and start manage server instances through admin console. But why it is failing only when i try to stop.could anybody help me on this

Stopping Weblogic Server...

Initializing WebLogic Scripting Tool (WLST) ...

Welcome to WebLogic Server Administration Scripting Shell

Type help() for help on available commands

Connecting to t3://jipsl13t:12001 with userid weblogic_admin ...
This Exception occurred at Fri Jan 18 12:20:09 GMT-00:00 2013.
javax.naming.AuthenticationException [Root exception is java.lang.SecurityException: User: weblogic_admin, failed to be authenticated.]
        at weblogic.jndi.internal.ExceptionTranslator.toNamingException(ExceptionTranslator.java:42)
        at weblogic.jndi.WLInitialContextFactoryDelegate.toNamingException(WLInitialContextFactoryDelegate.java:788)
        at weblogic.jndi.WLInitialContextFactoryDelegate.pushSubject(WLInitialContextFactoryDelegate.java:682)
        at weblogic.jndi.WLInitialContextFactoryDelegate.newContext(WLInitialContextFactoryDelegate.java:469)
        at weblogic.jndi.WLInitialContextFactoryDelegate.getInitialContext(WLInitialContextFactoryDelegate.java:376)
        at weblogic.jndi.Environment.getContext(Environment.java:315)
        at weblogic.jndi.Environment.getContext(Environment.java:285)
        at weblogic.jndi.WLInitialContextFactory.getInitialContext(WLInitialContextFactory.java:117)
        at javax.naming.spi.NamingManager.getInitialContext(NamingManager.java:667)
        at javax.naming.InitialContext.getDefaultInitCtx(InitialContext.java:288)
        at javax.naming.InitialContext.init(InitialContext.java:223)
        at javax.naming.InitialContext.<init>(InitialContext.java:197)
        at weblogic.management.scripting.WLSTHelper.populateInitialContext(WLSTHelper.java:520)
        at weblogic.management.scripting.WLSTHelper.initDeprecatedConnection(WLSTHelper.java:573)
        at weblogic.management.scripting.WLSTHelper.initConnections(WLSTHelper.java:313)
        at weblogic.management.scripting.WLSTHelper.connect(WLSTHelper.java:203)
        at weblogic.management.scripting.WLScriptContext.connect(WLScriptContext.java:61)
        at weblogic.management.scripting.utils.WLSTUtil.initializeOnlineWLST(WLSTUtil.java:147)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.python.core.PyReflectedFunction.__call__(Unknown Source)
        at org.python.core.PyMethod.__call__(Unknown Source)
        at org.python.core.PyObject.__call__(Unknown Source)
        at org.python.core.PyObject.invoke(Unknown Source)
        at org.python.pycode._pyx4.connect$1(<iostream>:16)
        at org.python.pycode._pyx4.call_function(<iostream>)
        at org.python.core.PyTableCode.call(Unknown Source)
        at org.python.core.PyTableCode.call(Unknown Source)
        at org.python.core.PyFunction.__call__(Unknown Source)
        at org.python.pycode._pyx15.f$0(/product/jip/jipsl11t/wls/eni132_domain/shutdown.py:6)
        at org.python.pycode._pyx15.call_function(/product/tsm/jipsl11t/wls/eni132_domain/shutdown.py)
        at org.python.core.PyTableCode.call(Unknown Source)
        at org.python.core.PyCode.call(Unknown Source)
        at org.python.core.Py.runCode(Unknown Source)
        at org.python.util.PythonInterpreter.execfile(Unknown Source)
        at weblogic.management.scripting.WLST.main(WLST.java:124)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at weblogic.WLST.main(WLST.java:29)
Caused by: java.lang.SecurityException: User: weblogic_admin, failed to be authenticated.
        at weblogic.common.internal.RMIBootServiceImpl.authenticate(RMIBootServiceImpl.java:116)
        at weblogic.common.internal.RMIBootServiceImpl_WLSkel.invoke(Unknown Source)
        at weblogic.rmi.internal.BasicServerRef.invoke(BasicServerRef.java:667)
        at weblogic.rmi.internal.BasicServerRef$1.run(BasicServerRef.java:522)
        at weblogic.security.acl.internal.AuthenticatedSubject.doAs(AuthenticatedSubject.java:363)
        at weblogic.security.service.SecurityManager.runAs(SecurityManager.java:146)
        at weblogic.rmi.internal.BasicServerRef.handleRequest(BasicServerRef.java:518)
        at weblogic.rmi.internal.wls.WLSExecuteRequest.run(WLSExecuteRequest.java:118)
        at weblogic.work.ExecuteThread.execute(ExecuteThread.java:207)
        at weblogic.work.ExecuteThread.run(ExecuteThread.java:176)
Problem invoking WLST - Traceback (innermost last):
  File "/product/jip/jipsl11t/wls/eni132_domain/shutdown.py", line 6, in ?
  File "<iostream>", line 22, in connect
  File "<iostream>", line 646, in raiseWLSTException
WLSTException: Error occured while performing connect : User: weblogic_admin, failed to be authenticated.
Use dumpStack() to view the full stacktrace

Done
Stopping Derby Server...