IncompatibleClassChangeError

I am using BCEL since one week, and I have a problems inserting a method in a method.
I want to insert in every method of every class, a method.
But my class doesn't work and I have a IncompatibleClassChangeError error and I don't understand from where, could be the error.
Sorry for my english.

this is my code:

try {
            JavaClass clazz = Repository.lookupClass("front.persistance.action.BlobClobInitAction");
            ConstantPool constants  = clazz.getConstantPool();
            cp = new ConstantPoolGen(constants);
            String nomStr = clazz.getClassName();
            nomClasseStr = nomStr.substring(nomStr.lastIndexOf(".") + 1) + ".class";

            //si les variables de la classe ne contiennent pas de logger
            //on insere partt
            Method[] methods = clazz.getMethods();
             //on parcours toutes les methodes pour les rajouter
             for (int i = 0; i < methods.length; i++) {
                 String methodeStr = methods[i].toString();
                 String nomMethodeStr = methodeStr.substring(0, methodeStr.indexOf("("));
                 nomMethodeStr = nomMethodeStr.substring(nomMethodeStr.lastIndexOf(" ") + 1);
                 if (!(nomMethodeStr.charAt(0) == '<'
                     && nomMethodeStr.charAt(nomMethodeStr.length() - 1) == '>')) {
                    Method stripped = ajoutLogger(new MethodGen(methods[i], clazz.getClassName(), cp));
                    if (stripped != null) {
                         methods[i] = stripped; // on écrase la méthode par celle recrée
                     }
                 }
            }
            clazz.setConstantPool(cp.getFinalConstantPool());
            clazz.dump(nomClasseStr);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }

    private Method ajoutLogger(MethodGen methodGen) {
        try {
            InstructionFactory factory = new InstructionFactory(cp);
            InstructionList instructionFinalList = new InstructionList();
            InstructionList instructionList = methodGen.getInstructionList();

            instructionFinalList.append(new PUSH(cp, nomClasseStr));
            instructionFinalList.append(factory.createInvoke("java.io.PrintStream", "println",
                    Type.VOID, new Type[] { Type.STRING }, Constants.INVOKESTATIC));

            instructionFinalList.append(instructionList);
            methodGen.setInstructionList(instructionFinalList);

            methodGen.setMaxStack();

            Method method = methodGen.getMethod();

            instructionFinalList.dispose();
            System.out.println(methodGen.getMethod().toString());

            return method;
        } catch (Exception e) {
            System.err.println(e.getMessage());
            return null;
        }
    }

Matthew

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