This article by Susan Cramm on the Harvard Business Publishing website is about IT projects but I think is even more applicable to KM projects. This is what she says:
In most cases, the benefits outlined in business (proposals) are a work of creative fiction, and, once the initiative is approved, they are filed and forgotten.
Smart leaders don't waste their time with this. They play the game, but they know how to make the game worth playing. They understand that only 30% of IT-enabled business initiatives deliver as expected and that the other 70% are plagued with unclear business objectives, missing-in-action executive support and inadequate user involvement.
It's a ritual that needs to played! Susan then offers some very sound advise in my opinion. The words below, especially the ones I have highlighted in bold are KEY. In short, business life is political :-)
To build support, it's important to align the initiative to the overall strategic business objectives and to align the initiative to serve the selfish interests of the individuals who will be impacted most.