the realation icon which is on the use case is disabled?why?
I’m not fully sure what you mean with “relation icon”; I assume you’re referring to the small arrow in the lower right corner which indicates that you have set up a sub-diagram?
Either way, those icons are model indicators. They’re used to show that there’s something extra “attached” to your model element. From the master & auxiliary view, sub-diagrams, an added description right down to an attached file.
Check the “view” tab, you’ll find an option called “Model indicator”; this controls whether these indicators are visible or not. Another way to do this is to right click on your diagram, find the “Presentation options” section in the pop-up menu, and select “Always Show Model Element Indicators”.
Hope this helped!