Administrative console throws error 500 with java.lang.NullPointerExcetion

Last Sunday, one of my friend got this problem.

Admin Console, when accessed, throws error 500 with java.lang.NullPointerExcetion.
SystemOut.log has the following entries

5ea42ee7 WebGroup I SRVE0180I: [adminconsole] [/admin] [Servlet.LOG]: /secure/logon.jsp: init
5ea42ee7 WebGroup I SRVE0180I: [adminconsole] [/admin] [Servlet.LOG]: /secure/layouts/browser_detection.jsp: init
5ea02ee7 WebGroup I SRVE0180I: [adminconsole] [/admin] [Servlet.LOG]: /secure/console.jsp: init
5ea02ee7 WebGroup E SRVE0026E: [Servlet Error]-[]: java.lang.NullPointerException
at org.apache.jsp._console._jspService(_console.java:172)

I found this technote http://www-01.ibm.com/support/docview.wss?rs=180&uid=swg21177893 regarding NullPointerException, which states -
Resolving the problem
To resolve this issue:

1. Clean up the disk space problem.
2. Delete the /wstemp//preferences.xml file.
3. Try to login to administrative console. This should build a new preferences.xml with the correct data and should allow the user to login to administrative console.

My friend followed these steps and resolved the problem.