Sdc29, am I correct in assuming that the four "official practice papers" are the computer-adaptive GMATPrep exams? Had you taken any of them before, or were you doing the four GMATPrep tests for the first time when you scored 44, 44, 47, and 42?
There could be a bunch of things going on here, but my hunch is that you might be a little bit inconsistent with your time management or you might be a little bit sloppy in general. On an adaptive test, careless errors are an absolute killer -- if you miss a couple of "getable" questions early in the section, you'll put yourself into a hole that you might never climb out of, since your score is based primarily on the difficulty level of the questions, not necessarily on the
number of questions you answer correctly. If you miss even one or two easy questions, you'll see more easy questions, and your margin for error can evaporate awfully quickly. I would wager that when you scored the 42, you missed a bunch of questions that made you yell, "How the %*#)!*%&!%*! did I miss THAT one?!?" at your computer screen when you reviewed the test afterward, and that's what did the bulk of the damage.
Again, there could be something else going on, but try going through all of your tests, and count the number of questions that you could reasonably classify as "careless" or "avoidable" mistakes. If the math was over your head or if you didn't understand the phrasing of the question, that's a different thing entirely. For now, just figure out how many questions looked like boneheaded errors. If you're making silly mistakes, you're much more likely to see crazy fluctuations in your score from test to test, and that's a sign that you need to really concentrate on rechecking your work and reading the questions extra-carefully before you jump into the math.
Of course, only two of your seven tests seem to stick out. So I might be barking up the wrong tree here. But at the very least, it won't hurt to take a closer look to see if sloppiness is costing you points.
Good luck with everything!