I know I'm getting in on this topic late, but I just started playing Cities XL 2011 a couple weeks ago. Anyway, I learned early on that when this happens, it seems to mean that the workers needed live too far away. For example, I built a motel on a highway surrounded by unskilled workers. The motel wasn't doing well, so I clicked on it and it told me it needed skilled workers. So I placed some skilled workers in the foothills across the street and as soon as they moved in the motel started making money.