Killing the messenger
Should you scare people away, they'll tell you only what you want to hear. Let it be known you welcome those who come bearing news, good or bad. You have a better chance of heading off the problem if you're approachable. When this happens, the severity of bad news you have to report to your boss is minimized. Ask plenty of questions, and confirm the facts backing up what he has told you. Feedback is vital for your survival.