There are different types of frames and the elements in oUF require a specific one in order to use their internal update process. Depending on the type of the
widget it has certain methods available. A good overview of the widget hierarchy could be found on
wowprogramming.com. Usually there is
some documentation in the top part of the element file that states the required widget. So, the health element requires you to define a key entry Health (i.e. Frame.Health) of the UI widget type "StatusBar". At Line 6 in your posted code snippet you define it as a simple "Frame", to which the SetMinMaxValues method, called in the elements internal update method, is not available.