title: JAR file: Could not find main class
body: <p>Okay, I have a strange problem. I wanted to run one of my programs as a .jar file, but when I open it by double-clicking it, I get an error message like &quot;Could not find main class, program is shutting down&quot;. I'm pretty sure I did everything right, the jar should work afaik. I also tried other programs, it's the same with every single one. (I'm creating the .jar's through BlueJ) There is no problem when I run them through a .bat . And here comes the strangest thing of all: The .jar's have worked some time ago (one or two months I guess), and I don't remember doing anything different. It's the same BlueJ-Version. Okay, maybe Java updated and something got messed up... I googled, but I couldn't find a solution. (some people seem to have a similar problem, and it seems to be only them who can't run their .jar's; they uploaded them and other people say the .jar's run fine.) What could be the problem? How can I solve it?</p>
  <p>I'd really appreciate some help here.
  Thank you :)</p>
  <p>EDIT: okay guys, you're making me unsure here. Imma check the manifest again, at this unholy time ( 1:34 am ) :P</p>
  <p>EDIT2: This is my MANIFEST.MF
  Manifest-Version: 1.0
  Class-Path:
  Main-Class: LocalChatClientGUI
  [empty line]
  [empty line]</p>
  <p>The Main class is correct.</p>
  <p>EDIT3: Thanks to hgrey: There is nothing wrong with the jar. I can run it from a bat file, which actually should not be different from double-clicking the jar, right? Yet I get the error when clicking it, and it works fine through the bat.</p>
  <p>EDIT4: I finally solved the problem. I re-installed the JRE and now it works, although I can't see any version differences.</p>
  <p>Thanks to everyone!</p>