Most managers fail for 4 basic reasons, or so believes Dan Coughlin, author of Accelerate: 20 Practical Lessons to Boost Business Momentum.  If you understand these root causes of executive failure and identify them early, successful leaders can mentor changes to prevent organizational problems.  Coughlin's 4 signs are:

1. Poor confidence.  Even smart people can lack confidence in their skills, and that negative persona can affect peers and subordinates alike.  One sure sign of poor confidence is a manager who continually changes their decision when faced with opposing viewpoints.
2. Poor communications.  Besides the inability to effectively share information, this trait can also be seen in negative behaviors such as rudeness, denegration of others, inability to accept good suggestions, and a know-it-all demeanor.
3. Poor judgment.  Do you have managers that continue to follow their own agenda even though the entire company is focused elsewhere?  Bad decisions do not necessarily only reside in actions related to customers.  Watch for activities that undermine your organization, its teams and its culture.
4. Poor direction.  Some people excel at generating ideas, however, their problem can be trying to execute every one of those ideas.  As leader, do you understand each manager's strategy and message?  Is it consistent?  Does it mirror the organization's direction?  If managers continually vascillate from the organization's mandate, lack of consistency will undermine your success.   

Successful leadership not only requires you to manage well, it also requires you to ensure your subordinate managers and leaders do so as well.  When you discover problems begin to crop up, that is the time to mentor the individual to a more success-oriented path.