Allan,
I've never used the particular button head screws that you describe, but another possibility is that the socket is some odd size and your wrench isn't that size. I have been bitten on that detail a couple of times. Evidently there are some odd metric sizes for the tiny socket head fasteners and the available wrenches don't necessarily fit. I have some wheel collars for which I don't have the proper wrench, and my choice is to either force a slightly oversize wrench into the socket or bugger the heads with a wrench that's too small. Third choice is to throw the collars away and get something that works better.
Dick