The different readings are perfectly normal. You will get a slightly different reading from different fingers or different meters and there is an 'acceptable' error of 10% I think. I had 8.1 and 7.5 this morning on consecutive tests. (I just average them, to be honest).
Control solution is a liquid that you test instead of using blood. The box that the strips came in (or the tub) will give a control range for the solution, i.e. it will say 6.1 - 8.2. If the meter reads within that range, then there is no problem. I have my doubts about control solution. If I do a reading and think it's wrong, I might do another and get a result that's quite a bit different. I then do a control test and it comes out as okay. Which number do I trust? From my personal experience if I don't like the number the meter tells me (i.e. I think I'm likely to be higher or lower) I do a couple of tests and take best out of three. Having said that, I'm T1 and have multiple strips on prescription so using 2-3 is not a real problem for me. I only generally retest if I'm around the hypo border and feel the number isn't right.
Despite looking beautifully and scientifically accurate and all that, with their lovely digital display and decimal point readout, they're not really that accurate at all, IMHO. What you're looking out for are trends over time. If you get a sustained rise in levels to, say, 12, then it might not be 12, it might be 11.5, but you know for sure that it's gone up.
If you think the meter is reading incorrectly, most manufacturers will swap a meter.
Hope that helps.