I use workflows with conditions to ensure a transition is not allowed if some extra data must be entered.
This works in terms that the transition button is not visible if it cannot be used, but how do I tell the user why they cannot do it?
The available options have pop-up help explaining what they do, perhaps if the unavailable options were shown, but disabled I could put something in the pop-up to help.
Perhaps I could display an annotated version of the workflow graph.
Even just a button to display a PDF.