Xaml cannot create an instance of “X”

This is because instantiating ApplicationsSettings throws an exception. If you add the following to your constructor, you should be fine;

try { settings = IsolatedStorageSettings.ApplicationSettings; } catch (System.IO.IsolatedStorage.IsolatedStorageException e) { // handle exception }

这是因为有可能出现异常，需要在构造函数中作出判断，抛出异常。