If you open a pre-Maya 2014 scene that renders using the mental ray for Maya renderer, your sampling settings are changed to use Unified Sampling. Some features, such as contour rendering, are not supported with Unified Sampling.
To render legacy scenes with their previously-saved legacy sampling settings, select the Legacy Sampling Mode or Legacy Rasterizer Mode in the mental ray Render Settings: Quality tab. If you are using command line rendering, you can also use the -sampling flag.
New presets are also available for Unified Sampling from the Render Settings Presets menu, including: Preview, Production, FinalFrameEXR.