Not enough relief on the neck.
Take it to between .3 and .5 mm (measured at the 9th fret, low E string with it fretted at the first and last frets).
This will help some with the buzz, but remember, no matter how well the frets are dressed/leveled, you will always have SOME buzz at low action (2 mm is considered low).
If you want no buzz at all you'll have to raise the action, or pick lighter. I've gone the higher action road myself. It's amazing, actually, my tone is better (to my ears) no buzzing and it doesn't take long to get used to it, and I have a weakened left hand/arm due to an injury from years ago.
Other than that, you'll just have to live with a little buzz here and there. Listen to a lot of recordings and you'll hear fret buzz from time to time, it just happens. :-)