I find that managing expectations up-front goes a long way with clients. I start every project with this, "Unlike what you've seen in the movies and TV, I can't quickly punch some keys and have your system flawlessly implemented in 5 minutes. Many forms of technology must interact with one another flawlessly to create a perfect system. Be advised, the first implementation will need to be tweaked. This is not a failure, this is the normal process." Then when I roll it out and the inevitable happens, no matter how major or minor, the client just repeats what I say, "This is normal, huh?" Always maintain your cool and don't blame anyone. It's all about managing expectations.