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Hard to say what is happening without seeing the full text of the error messages.

Probably not. I don't know why the program in your old jar file does not execute. I suspect it could be because of something that has been removed from the current version of java. If that is the...

The normal jar file does not contain the source files used to create the class files that are executed.
You will need to find all the .java files for the .class files contained in the jar file. ...