This error means that the current browser page does not have login and password input fields. Go to a page that has such fields and press the extension icon again.
In some cases the extension cannot detect login/password fields on a page. This happens on web pages with a bad HTML design, when real input fields are hidden under fake ones until you click on them or when they are placed in a popup. In such cases you can right-click on an input field and select SafeInCloud > Paste login or Paste password from the context menu.