This article posted on Infoq talks about the problems faced by a SCRUM/XP team and unfortunately, it all sounds too familiar.
One of the biggest problems facing the agile community is convincing the potential customer or product owner to take responsibility for their actions. This is partly a case of lacking education, most product owners don't come from a software development background and development teams need to be understanding and helpful in these cases.
Another major contributor however, is that they have no motivation to collaborate. Most of these people are used to working on failed/failing projects and as soon as they see where the process is headed realize that they are actually supposed to do something, and doing something means opening themselves up to potential blame when things go wrong. I think there are numerous reasons - including lack of knowledge of the product itself, lack of vision of where they want it to go and fear of blame in the event of failure. In many ways, I cannot blame such individuals, its human nature and one of those situations I can't think of an easy way out of.
Oh well, not all problems can be solved!