Error in starting maven - nullpointerexception

When I run mvn --version I am getting the following error.

java.lang.NullPointerException: key can't be null
at java.lang.System.checkKey(System.java:773)
at java.lang.System.getProperty(System.java:649)
at org.codehaus.classworlds.Configurator.configure(Configurator.java:240
)
at org.codehaus.classworlds.Launcher.configure(Launcher.java:156)
at org.codehaus.classworlds.Launcher.mainWithExitCode(Launcher.java:426)

at org.codehaus.classworlds.Launcher.main(Launcher.java:375)

The following are the settings done for Maven
set JAVA_HOME=D:/java/jdk1.6.0_02
set M2_HOME=D:/ReadNew/apache-maven-2.2.1
set M2=%M2_HOME%/bin

After referring to the link (http://maven.40175.n5.nabble.com/Created-MNG-4865-mvn-fails-because-of-null-property-td3211656.html) I added the following entry in m2.conf
set MAVEN_OPTS=-Xmx1024m -XX:MaxPermSize=256m

But still the error persists.
Could someone help me in resolving the same.