Here is one tip for your UI design that can really make life easier for your users: “Why is that button gray?” – or smart tooltips for disabled elements.
One additional comment: The tooltip shows a lot of information why the button is disabled. Why not simply set the right tooltip in the save place where you disable the button? At that time, you’ll know exactly why you do it and you can give the user specific directions what to do now (instead of having her read and pick from a list).
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