Running jar file gives error message

I'm running the Java 2 SE, 1.3.0_01, on NT 4.0. I have VisAD installed
in \JDK\demo\VisAD

I'm trying to run VisAD =.jar using a batch file located in the above
directory, and containing the line:

java -jar visad.jar

I get an error message reading:

Failed to load Main Class Manifest attribute from visad.jar

What am I missing?