One thing i've learned (at least for me, maybe i'm doing it wrong) If i want a 64x64 sq tiled BG , I make the image 65x65 and paste it onto a 64x64, in my editor. Not rich enough for photoshop yet. Seems C2 likes to add a pixel of padding around the image, even after you crop it in C2.
Or if you have the 64x64 tile, try and stretch it out 1px on all sides.
It's just trial and error.