Looking at the code I see that the browser's object is being used for the navigate method. Using the Object you are accessing the native methods and properties of the object. Using Internet Explorer and UFT spy I do not see a navigate in the native methods. UFT does have a navigate method using the Browser object. Recommend changing your code to use the Browser object instead of the Browser().Object objects.
For more information check the Object Model Reference For GUI testing > Web > Browser Object > Navigate.