As no one else is answering this ;-)
I really would need to see the command you are executing and the jar , class path , as its a little confusing as to what you intended and therefore as to what has gone wrong... but did you actually want to define a main class in the jar.
It almost sounds like you are using
java with the -jar option when you didn't want to use a jar in this way i.e. you just wanted the jar to be on the classpath i.e using -cp -classpath.
The error means you have told java that you wish to execute one jar file (with possibly others on the classpath) when you execute java in this way it opens the manifest looks for the line that defines the main class and then attempts to load it from the jar in your case its failing to find it. Your not trying to execute one jar but have the main class specified in another jar ??
You mention compiling which is the javac command I wasn't aware that could give the error mentioned ... any one ??
"Eagles may soar but weasels don't get sucked into jet engines" SCJP 1.6, SCWCD 1.4, SCJD 1.5,SCBCD 5