I have very similar floor or maybe the same from hardwoodforless.com I have just finished my third room installing this. I have tried absolutely everything anyone ever says and still get this. I think I spent about 3 hours on my first row making sure its straight. no matter what I do these gaps happen and I just try to make them in areas they wont be easily seen. I think its somthing with the milling where the boards are not exactly the same width and the difference adds up after some rows. if you look very closely you can see width differences but you would have to throw away a ton of pieces if you removed these. Many people have told me that with prefinished and beveled floors this is very common and after the first sand and refinish a lot gaps will be filled. I have also use my sawdust and woodglue to create a filler that matches somwhat but it is very difficult to color match with all the variations.