The way I understand it is that the problem is with the definition of velocity. If you want to measure speed, you have to measure distance, which eventually comes down to the magnitude of the vector between two points - subtract the X's, subtract the Y's, subtract the Z's. Problem is, at cosmic scales, expansion means that those two points aren't in the same reference frame, because more space has appeared between them. You can try to measure it, but by the time you do the axes themselves have stretched again. The two X's can't be subtracted directly anymore, because they're on different reference frames. You get a result of >>C only by assuming that the relevant bits of space are relatively well-behaved Euclidean R^3, but that's not the case.