[nitro]

I also get this error. I don't know what is wrong but when I start it from the command line I get a different error:

$ java -jar textg.jar 
java.lang.UnsupportedClassVersionError: Bad version number in .class file
********at java.lang.ClassLoader.defineClass1(Native Method)
********at java.lang.ClassLoader.defineClass(Unknown Source)
********at java.security.SecureClassLoader.defineClass(Unknown Source)
********at java.net.URLClassLoader.defineClass(Unknown Source)
********at java.net.URLClassLoader.access$100(Unknown Source)
********at java.net.URLClassLoader$1.run(Unknown Source)
********at java.security.AccessController.doPrivileged(Native Method)
********at java.net.URLClassLoader.findClass(Unknown Source)
********at java.lang.ClassLoader.loadClass(Unknown Source)
********at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
********at java.lang.ClassLoader.loadClass(Unknown Source)
********at java.lang.ClassLoader.loadClassInternal(Unknown Source)
Exception in thread "main"

Which JDK version did you use to compile this program?

EDIT:
I just recompiled and repackaged your code with the same manifest so that's not your problem. I did get a notice during the compilation

Note: GUI_Textg.java uses or overrides a deprecated API.
Note: Recompile with -Xlint:deprecation for details.

I think something strange has happened when you compiled the program.
BTW I'm using Sun JDK 1.5.0_09