A problem is something you can do something about. If you can't do something about it, then it's not a problem, it's a predicament. That means it's something that must be coped with, endured.
Upon the solution of this problem, or upon sufficient proof of the impossibility of synthetical knowledge a priori, depends the existence or downfall of metaphysics.
It isn't that they can't see the solution. It's that they can't see the problem. They can't see the problem if they are looking in the wrong place. They can't see the problem if they have blinders on - for 'none are so blind as those that will not see'.