This is weird.  I have a swing app that I cannot run in 6.5, it might not be a compile problem but there was not a run
component.
I have a project I made with 6.1.  It includes a few thousands source files and several jar files under libraries.
The project works fine in NB 6.1. 
When I try to run the project in 6.5 I get the error below.
I go back to 6.1, and do a clean recompile and it will run.  If I don't do a clean recompile, it will NOT run back in
6.1. (Same error)
My jdk is J6 Update 10 RC.
You can reach me via email (brian@gabey.com) for questions or for me to try things to help narrow it down).

run:
java.lang.ClassFormatError: Absent Code attribute in method that is not native or abstract in class file
com/teseda/ui/ewb/EWB
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:621)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
        at java.net.URLClassLoader.access$000(URLClassLoader.java:56)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)