iOS SDK 2.X 升级 3.1.0，数据库升级迁移失败

我在 appdelegate didFinishLaunching 调用的，在注册 appkey 之前之后调用
[EMClient sharedClient] dataMigrationTo3]  都失败。有可能是什么原因呢？大神给分析下吧！感谢！
代码如下：

    if([[i][b][EMClient sharedClient] dataMigrationTo3][/b][/i])

    {

        MLog(@"EaseMob db update success ~~");

    }

    EMOptions *options = [EMOptions optionsWithAppkey:EMAppkey];

    [[EMClient sharedClient] initializeSDKWithOptions:options];

    [[EMClient sharedClient] addDelegate:self delegateQueue:nil];//登陆相关的回调

    [[EMClient sharedClient].groupManager addDelegate:self delegateQueue:nil];//群组回调

    [[EMClient sharedClient].chatManager addDelegate:self delegateQueue:nil];//消息回调