Gorilla会话文件系统存储找不到会话文件

I'm starting to build a regular web app with golang and Angular2, and most importantly I'm trying to secure my login with the help of auth0.com. I download the quickstart code from here and try to run the code, it worked for a while and then next time I run it, the /tmp/session file cannot be found any more.

Here are some basic idea of the code auth0.com provides.
1. Initialize the gorilla sessions filesystemstore
2. Then start the authentification process
code is provided below

app.go

var (
    Store *sessions.FilesystemStore
)

func Init() error {
    Store = sessions.NewFilesystemStore("", []byte("something-very-secret"))
    gob.Register(map[string]interface{}{})
    return nil
}

login.go

func LoginHandler(w http.ResponseWriter, r *http.Request) {

    domain := os.Getenv("AUTH0_DOMAIN")
    aud := os.Getenv("AUTH0_AUDIENCE")

    conf := &oauth2.Config{
        ClientID:     os.Getenv("AUTH0_CLIENT_ID"),
        ClientSecret: os.Getenv("AUTH0_CLIENT_SECRET"),
        RedirectURL:  os.Getenv("AUTH0_CALLBACK_URL"),
        Scopes:       []string{"openid", "profile"},
        Endpoint: oauth2.Endpoint{
            AuthURL:  "https://" + domain + "/authorize",
            TokenURL: "https://" + domain + "/oauth/token",
        },
    }

    if aud == "" {
        aud = "https://" + domain + "/userinfo"
    }

    // Generate random state
    b := make([]byte, 32)
    rand.Read(b)
    state := base64.StdEncoding.EncodeToString(b)

    session, err := app.Store.Get(r, "state")
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }
    session.Values["state"] = state
    err = session.Save(r, w)
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }

    audience := oauth2.SetAuthURLParam("audience", aud)
    url := conf.AuthCodeURL(state, audience)

    http.Redirect(w, r, url, http.StatusTemporaryRedirect)
}

The Error log is

open /tmp/session_46CNLLHBKD... : no such file or directory

I try to understand the code and findout that error log comes from login.go line 39(session, err := app.Store.Get(r, "state")). And I started to track down the code and find out.
login.go:39 -->store.go: 180-->session.go:132-->store.go:186-->store.go:272
you can find store.go and session.go here.
The error log comes from this line: fdata, err := ioutil.ReadFile(filename)
Through the whole process I have not found any function call to save the session file.

I don't understand this error and I don't know why I can run the code at the very beginning, please help me with this problem.
Your any suggestion will be greatly appreciated.Thanks a lot.

I figure out the answer myself

It turns out that I changed my secret key while initializing the gorilla session filesystemstore, but I have not deleted my cookie file in chrome, so it cannot find the tmp sesiion file needed.
I change the key, then delete the coorsponding cookie file and everything is ok now.