The article Software Project Risks and Development Focus by James J. Jiang & Gary Klein published in PMIs PM Journal March 2001 identified the following as the most frequent causes of project failure:
1. Project Size (# people)
2. Application Complexity
3. Technology Acquisition
4. Insufficient Resources
5. Lack of team expertise
6. Lack of user support
7. Lack of user experience
8. Lack of clear role definition
9. Intensity of conflicts
The best way in general to approach this is to define robust processes to manage projects. Since application complexity is an issue, encourage the team to look for ways to simplify the application or phase out the work. If there are insufficient resources and/or expertise, work with the HR department or resource manager to document your needs and step up recruitment. Defining clear roles and responsibilities will also help minimize some of the conflicts.
In general, notice these causes of failure all center on people issues. As a PM you will need the management skills and soft skills to handle these.