Harry Reid has been pissing off Willard M. Romney in a big way by suggesting he did not pay any taxes at all in some or all of those years for which he won't release his returns. Harry was selected to make the effort, of course, because he's a fellow Mormon. Nobody can claim religious discrimination.
Romney says he obeyed all the laws, etc., and I'm sure he did. Probably he did pay some taxes in some of those years. It's not Romney's personal taxes that cannot be revealed, however. More generally, it's just what the taxes the super-rich tend to look like. You can't have your ordinary American getting a gander at that, after all.
Somebody might notice how the rest of us are being screwed.