when using a complex sketch, sometimes, it's hard to find what is stopping you from specifying a dimension. It may be measurements from origin, or from other points or lines, or it may be parallel or perpendicular or angular constraints. Is there a way to see what is causing the issue? It would be need if there were a button on the pop-up derived dimension notification "Show constraints" and it would highlight them in red on the sketch (or something like this).
