Classnotfoundexception eventhough the class is inside jar

Hi guys,
I encountered weird problem where sometimes it throws classnotfoundexception eventhough the class is inside jar. I terminate the program and start it again then it works fine. I compiled the jar using ant
     <target name="compile" depends="clean" description="">
           <echo message="using java version    : ${java.version}"/>
           <echo message="using ant.java.version: ${ant.java.version}" />
             <javac srcdir="${src.dir}"
                    destdir="${build.dir}"
                    debug="on"
                    source="1.5"
                          excludes="com/csg/cs/mud/junit/*"
             />
            <jar destfile="${mmd.jar}"
                 basedir="${build.dir}"
                 excludes="org/css/cs/mmd/juni*,org/css/cs/mmd/utility/MDDClient.class"
            />
     </target> it shows :
*[echo] using java version : 1.5.0_04*
*[echo] using ant.java.version: 1.5*
and I deployed this jar to sun solaris (SunOS sg123-456 5.8 Generic_117350-44 sun4u sparc SUNW,Ultra-80) and sun solaris box is using jre1.5.0_06.
Appreciate any advice please. thanks in advance!
Cheers,
Mark
Edited by: kmthien on Aug 2, 2010 3:05 AM

Is it public?
Is it spelt correctly, and the same, in the jar file and the code?
Is it in its correct package in the jar file?
Why are you excluding a class from the jar file?

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