Suppose you have an error:
invalid or corrupt jarfile
Or related one:
Error: Could not find or load main class com.test.package.Main
The first thing you need to do is to check your main class defined in manifest.
If you’re 100% sure that everything is all right, then check any running JVM processes, associated with that file and kill them.
The thing is that you probably ran the old version of the jar, and forgot to stop it. Even if you’ll replace the file itself with the new version, it won’t work, as long as you have your old version running in JVM.
If you still have any questions, feel free to ask me in the comments under this article, or write me on firstname.lastname@example.org.