this can be the result of some sharpening. It's very easy to avoid these borders:
Do all your image-procedures like you used to do before (Photoshop CS3 in my case).
Resize your image to (in case you want 1200x800 as final size) to 1203x802 (3:2 crop).
Final Step: Resize Canvas: 1200x800 -> OK
-> Proceed -> ....
.... result -> no borders