When you select Animation->Make Movie, in the dialog box that comes up click on the Quality box and change it to Current Render Setting (as in the attached pic, click it to make it bigger) and then it should render properly.

Other advice would be to render to image files (same dialog box, this time Sequence Type and choose Image Files) as if your render fails halfway through for any reason, you can then resume rendering from the frame it stopped at. You would need to assemble the frames into an animation with another program though and also add the sound after too.