I have 2 issues of doctrine with Rick Warren and his "40 Days of Purpose" curricula.
My core problem with 40 Days of Purpose centers upon the nature of gospel that it advocates. I believe its gospel is semipelagian, meaning that it adds human works to the work of Christ rather than encouraging believers to trust wholly in Christ for complete justification, sanctification, and reconciliation. The former misrepresents the predicament of human beings and therefore incorrectly administers the remedy. Further, it misrepresents the work of Christ, and therefore misapprehends the object of faith, namely Jesus himself. This is a dangerous error, and one not to be handled lightly or simply dismissed because "it works."
My secondary problem with 40 Days of Purpose is that its author, Rick Warren, incorrectly handles the Scriptures. Many object offhand to his use of various translations, I am not concerned about this. There is nothing wrong with using different translations as long as the aim is right. Is the aim to support your point or to correctly teach the point of the biblical author? Anyone who wishes to submit himself to God as a faithful teacher of the Word knows that attention to the point of the author is paramount for proper understanding. Deviation from that point, even for the most benign reason, results in an instructive word coming not from the mouth of God, but from the heart of man. "The heart is deceitful above all things, and desperately wicked." (Jer. 17:9) The Scriptures are very plain, God does not brook false teachers. Every teacher and pastor should daily tremble at the warnings plainly given for anyone who knowingly distorts the Scriptures. And, indeed, with the number of translation helps, electronic and in print, and commentary sets, as well as New Testament or Old Testament scholars only too happy to answer any questions a pastor may have, there is no excuse for not trying with all of one's energies to preach God's word in the churches.
Therefore, I find Rick Warren without excuse. Seminary trained, and wealthy enough to hire what he does not personally possess due to constraints in time or temperament, I believe he is responsible to both of these charges. And how is this not all the more so with the explosive success of his programs throughout the world? If there is any question or doubt, even the smallest point of inaccuracy, shouldn't each instance have been exhaustively dealt with at this point simply because of the world-wide reach of this preached word?
One might as that errors are understandable, saying that Rick Warren is just a human being. I understand this, as far as it goes, but argue that the errors of which I speak are not few in number, nor do they spring from "hard texts," passages which may cause disagreement among the most faithful and careful exegetes. Rather, they are at best hermeneutically sloppy and at worst evidence of an eisegetical approach to Scripture which bends the authority of God to the desires of men.
I believe that both of these charges which I have made may be discerned through a careful investigation into the use made of Hebrews 11:6 by the Purpose Driven curricula.
 There is no doubt that there is a good bit of practical wisdom in the structural advice provided by Rick Warren, and especially in his book The Purpose-Driven Church. I have no issue with this, nor am I responsible for discernment in this area. My burden is the gospel: that in all things I would love, protect, promote and pursue the gospel to the best of my abilities both for myself and for the good and salvation of my fellow human beings.