"Invalid or corrupt file" after Obfuscation with "The Marvin Obfuscator"

Question

Hi!
I want to use "The Marvin Obfuscator" (www.drjava.de) to secure MY code a little bit.
But the resulting .jar-file doesn't work. "Invalid or corrupt file".
I think, that things, i configured in the configuration file aren't true.
Has anyone experience with "The Marvin Obfuscator"?
I created a .jar-file with Eclipse. My Marvin-configuration-file (config.txt) is as the following:
// Template for a Marvin Obfuscator config file
// Directories and jar/zip archives where your application's classes reside
// (relative to project directory)
classpath=("archive.jar","C:\Java\jre1.5.0_05\lib\rt.jar")
// The name of your applet or applications's main class
// (e.g. executable class, servlet or applet)
// (as it would appear in <applet code=...> or in "java ...")
// Note the double parentheses!
mainClasses=(("control.Start"))
// If you want your main class to be called differently after the obfuscation,
// you can enter the new name (including package) like this:
// mainClasses=(("myapp.Main" newName="main"))
// You can also have more than one main class:
// mainClasses=(("myapp.ServletA") ("myapp.ServletB"))
// Names of methods (without class name) that are accessed via reflection.
// The obfuscator will not change the names of these methods.
//preserveMethodNames=("methodName1","methodName2","reflected*")
// Classes that are accessed via reflection.
// The obfuscator will not change the names of these classes.
// Note: Method names within these classes will still be obfuscated.
// (If you need to preserve method names too, what you probably want
// is "externalClasses".)
// Note: You can use the wildcard character (*).
//preserveClassNames=("mypackage.SpecialClass")
// Classes that are used by your application,
// but should not be included in the obfuscated jar file.
// The obfuscator also ensures that references to these classes continue to
// work ("referencing" includes calling, subclassing and implementing).
// Note: Any part of these libraries that is actually used must be in the
// classpath (either system classpath or classpath= line in this file).
//externalClasses=("com.company.externallibary.*","org.apache.*")
// Locations of resource files.
// If you want resource files (images, properties files, ...) to be included
// in the jar file, specify the resource directories or archives here.
// Do NOT specify individual resources files (these will be interpreted as
// archives).
// Note: Directories will be scanned recursively.
// Note: .class files are excluded automatically.
// Note: You will usually want to reuse entries from the classpath= line
// (classes and resources are often bundled in the same jar files).
//resources=("resourcedir","resources.jar")
// Advanced obfuscation features.
encryptStrings=true // You can try to set this to false for troubleshooting

Answer 1

Why not use another obfuscator? Google for "java obfuscator". I myself
use JShrink and it does a good job in reducing the code size.
It always generated valid class files for me.
As for "protection", don't count on it too much with any obfuscator, but
yes, some may do a better job than others.