what's wrong with unwrap seams in normal map

dic1405

I'm a student and have just started with the baking technique.
The edges where I made seam to unwrap just appear like this when I add normal map, I dont know why when I render to texture for the map, it just got this result:poly141:

And when I open the light map and normal map I found that the two maps dont look like they fit together. Im using 3dsmax 2013 64bit

uncle

I think the problem is caused by white background in normal map, probably caused by alpha. Those white stripes on dilated edges give those shading problems, 127 127 255 color background may fix this.