A few things: 1) You need to increase the edge padding, that should get rid of the black lines. Here is a polycount wiki entry that helps explain what's happening. 2) Since you're rendering in MR, you might as well just render out a AO map instead of a diffuse map. When you pick the map output type, select MR AO instead of…
I'm using 3d max 2012 and i'm doing render to texture with render Metal Ray and i'm using almost default settings at this point with only differences with samples being at 1,000 and element background being black. my materials are setup to render to diffuse and i've got Ambient Occlusion in that slot.
MentalRay fudges up the edge padding if you bake more than one map type at a time. Get rid of all but one output and it will get it right. So if you're baking, normal, diffuse, spec and AO, you have to remove all but one from the list, render that one map, remove it and add the next one. Wash rinse repeat until you have…