Error fetching Information from SharedPreferences Android

I have an android application, and in it I save some basic user information in SharedPreferences, however I started to display the following JSON parse error:

  

java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 2 path $

Codes:

Class for Handling SharedPreferences:

public static void setPreferences(Context ctx, String key, Object value) {

    pref = ctx.getSharedPreferences(arquivo, 0);
    editor = pref.edit();

    key = key.toLowerCase();

    if (key == null || value == null) {
        return;
    }
    Gson gson = new Gson();
    String json = gson.toJson(value);
    editor.putString(key, json);
    editor.commit();
}

public static String getPreferences(Context ctx, String key) {
    pref = ctx.getSharedPreferences(arquivo, 0);
    String obj = pref.getString(key, "");
    return obj;
}

Save Something Code:

Note: I convert everything to Object before saving.

 Gson gson = new Gson();

 //Recupero o Objeto para editar o que tem gravado
 String aux = SharedPreferences.getPreferences(ctx, "configuracao");
 Configuracao c = gson.fromJson(aux, Configuracao.class);

 //Salvo Novamente
 SharedPreferences.setPreferences(ctx, "configuracao", c);

The first time I save, it works fine, however when I try to get it from SharedPreferences it throws the exception above when casting:

SharedPreferences.setPreferences(ctx, "configuracao", c);

Configuration Class

public class Configuracao {

        private String ip;
        private String porta;
        private String caminhoWebService;

        public Configuracao(){
        }


        public String getIp() {
            return ip;
        }

        public void setIp(String ip) {
            this.ip = ip;
        }

        public String getPorta() {
            return porta;
        }

        public void setPorta(String porta) {
            this.porta = porta;
        }

        public String getCaminhoWebService() {
            return caminhoWebService;
        }

        public void setCaminhoWebService(String caminhoWebService) {
            this.caminhoWebService = caminhoWebService;
        }


}

The first time I save the configuration object and call getPreferences then the object comes like this: // It works

{"caminhoWebService":"http://192.168.254.8:8084/UltraMensagensREST/recursos"}

If I make a set again, replacing what was written, and call a get again, comes this in return: // throws the exception

 "{\"caminhoWebService\":\"http://192.168.254.8:8084/UltraMensagensREST/recursos\"}"

In this case, throw the exception above.

Does anyone know what it can be?