Upper management provides little or no support for lower management and project managers.
Even with a great plan, if adequate resources are cut off from the colleagues who need it, the project will stagnate. In addition, if decision making is required from the top, managers will be constrained and delayed if higher management fails to be attentive.
Not only is it important for lower management to be stay in communication, but for upper management to understand the obstacles and make an effort to answer questions in a timely manner. If projects are cooperatively attended to by upper and lower managers, then cost/scope/time issues can be prevented.