“Invalid signature file” when attempting to run a .jar

Question

My java program is packaged in a jar file and makes use of an external jar library, bouncy castle. My code compiles fine, but running the jar leads to the following error:

Answer 1

This happened to me in Intellij when I clicked "Add as a Maven Project" on bottom line when Intellij said "non-managed pom files found.". Meanwhile out folder was already generated. So it did not get recent changes.

Deleting out folder and running the program solved the issue for me. out folder was then recreated.

See the answer of Little Fox as well. The error I received was very similar to his.