Hello,
It looks like you have a few faces that aren't pointed in the right direction, which is why they are gray. First you should look at the direction of your object normals.
A good way to do this in Maya is to turn on
backface culling - this makes it so that when you view the object in shaded mode the back sides of every face are see-through. I'm not sure which option does this in Blender and 3DS max but I bet someone on here does.
If the normals are OK, then check for
non-manifold geometry - Sometimes, when I get a 3D model handed to me that was made originally in a different package the component information (or 3D object DNA

) goes funky and weird things happen. Non-manifold geometry can be one of those things. Basically it's when you end up with two faces stacked right on top of one another instead of one. It's easy to fix but hard to spot sometimes. To locate non-manifold geometry in Maya you open up the
cleanup command under the
mesh menu, activate
select non-manifold geometry and hit OK. Whatever faces that are left selected are your trouble spots. To fix in Maya, delete the trouble face/faces and use
append poly to fill in the gap left over.
Another reason you may be seeing the red lines is because the four vertices of those faces aren't merged (or welded) to their buddies in the same spots. So your object is considered open. Again, if that face isn't pointed in the same direction as it's neighbors (inverted normals) the verts won't merge and you'll have red lines (indicating a floating face) and gray color (indicating the back side of the face)