Java SE (Java Platform, Standard Edition)

Greetings, I have this Internal Frame SWING UI that works on my other computer perfectly, I copied the .java to this one that has the latest JDK 1.5.0_03, but whenever I try to compile it, this error comes up

"Eliminar.java": C:\Documents and Settings\progweb\jbproject\apoyo\Eliminar.java:7: cannot access javax.swing.JInternalFrame,bad class file: C:\Program Files\Java\jdk1.5.0_03\jre\lib\rt.jar(javax/swing/JInternalFrame.class),class file has wrong version 49.0, should be 48.0,Please remove or make sure it appears in the correct subdirectory of the classpath. at line 7


I browsed through rt.jar and JInternalFrame IS inside.

I get issues with ANY SWING Component, JInternalFrame, JDIalog, etc it says the same rt.jar wrong version.