Project Management

Are these “certain people” Black Belts that fall under your pervue?   If so, it may be time to wield the hammer of accountability.   Did they sign a charter/contract?   If so, leverage it to the hilt.   Many Companies have wisely held charters/contracts as legally-binding documents.
If you are matrixed, you may need to have a “come to church” session with them and their “solid-line” boss(es)/Sponsors.
This is really about leading/influencing people, not so much about managing their projects.
-My $0.02

Curious George,
Find out why those “certain people” aren’t doing things the way they should be. Are they properly aware of their responsibilities/deadlines? If yes, then are they constrained by their skill, their will/inclination or time bound issues? Find these first. Based on this you should choose how to motivate the people.
People with time issues can be sorted out easily with a little use of common sense. People, who are skill constrained, need to be properly trained, mentored and coached to bring them up to the performance levels necessary. A good leader not only gets performance out of his colleagues/team members, but also contributes to their development along the way.
The ones with willingness/inclination issues, would be tricky, but they aren’t (or shouldn’t be) impossible. Talk to them, interact with them more often, and find out why they lack interest. Should you find they do not identify with SS/Lean/Continuous Improvement, maybe your organization didn’t spend the needed time on awareness about them. You’d have to do this then. Focus on how it helps the organization as well as the employees involved. Show it to them as a path to greater roles & responsibilities, recognition and rewards. Get to their ulterior motives and use that to highlight the importance of your projects. Market your project, heck… sell your project to them showing them that it will benefit them the most!! Once you are able to establish a direct correlation between your projects and the employees’ goals… you have all the aces! Thereon, all you need is to lead from the front and keep guiding the others. It’s a project in continuous improvement in itself!!
Please ensure that you’ve tried everything else in the world before using “heavy-hand” tactics!

Agreed, the heavy-hand is a last resort.   If I understood the original post, this has been an on-going “battle” of sorts.   If so, the H^2 may be called for, after of course, trying to determine the RC of the encountered resistance.   The resistance typologies can help you root out the source of said resistance and help plan for overcoming it.
Bottom line, what’s in it for them?   What’s the payoff for their efforts?
if that doesn’t work, then yes, leverage the heck out of your charter/contract.

I appreciate the “Never surrender” approach, especially as applied to 6S, but it is also wise to know when to fish and when to cut bair.
Persistence is indeed a rare virtue these days, but persistence and “keep on trying” attitude isn’t a guarantee of success either.   This is where your change agency/OD skills will come into play.   This where your political saavy will make or break your ability to influence.
As the classic Kenny Roger’s song goes, “You got to know when to hold ’em, know when to fold ’em…Know when to walk away, know when to run..You never count your money, when you’re sittin’ at the table, there’ll be time enough for countin’, when the dealin’s done…”

I also think the “little things” are important too. For example, when was the last time success (big or small) was recognised and celebrated as a team? When someone did a good job, were they told they did a good job so that they knew whatever they delivered was what was required? When someone doesn’t deliver, were they told exactly what was the shortfall? And was the feedback done immediately? Is there sufficient trust built between you and your individual team members such that any suggestions coming from you are constructive and not as a means of “having a go” at them?
In my personal opinion, I believe that 9/10 (I never measured this – ha ha) of people want to to a good job. But they need to be told exactly what they are doing right or what needs to be done (and less of what what they are doing wrong).
Cheers.

I agree that getting to know each one can help you select the best strategy to use with each.  Do you do a stakeholder analysis on the team members when you start a project?  Defining what risk lack of commitment posses to the project, how important they are to the success of the project, and factors that may influence their behavior, can help you define the right strategy for each.  In this case, it sounds like you are getting push back from some people “consistently”.  Causes me to ask why they are assigned to the project in the first place; that might be an influencing factor to help you set your strategy.  In some cases, the timing is not right for them to accept this commitment, and for the sake of the project benefits the company is counting on — have a frank discussion with them (make sure you are speaking with facts and not emotion), and get on with it. 
Tolerating sabotage is never a smart move. 

Let me share my experience.
During the first meetings, team members, (new to six sigma) were skeptical about it, no cooperation at all. By the end of the project, everybody became fan of six sigma.
So, I guess, everybody must see it works.
Silviu
 

You did say you were a MasterBlackBelt, correct? What am I missing here????