Your machine probably isn’t using Java to run the jar, and is trying to run it with something else. First, make sure you have Java installed. You can check this by going into your system settings and verifying that a ‘Java’ application is there (Windows: Control Panel->Java, OSX: System Preferences->Java, *nix: Terminal->java -version).
If Java is not present, install Java from here or using a package manager such as aptitude or pacman with the address default-jre.
Java is present and you are on windows, can run this application Download here to fix your problem.
After running that, try re-running the Podcrash+ installer jar. It should open fine.
If you are on OSX, first put the .jar file in your Downloads or another folder which you know. Go to your Applications and run Terminal. Then, in Terminal, type the following then hit enter:
java -jar ./Downloads/Podcrash+_b1.4-Installer.jar
If it says something along the lines of Java is not installed, rerun the installer linked above.
If you put the .jar file in a directory that is different from Downloads, change the Downloads to whatever folder you put it in.
On *nix systems such as Linux and Solaris, go to Terminal and run chmod +rwx ./Downloads/Podcrash+_b1.4-Installer.jar (assuming the .jar is in your Downloads and you are running from ~), then run java -jar ./Downloads/Podcrash+_b1.4-Installer.jar.