It's not an error with the rom. That app is not authorized for streaming on the A500 ICS build yet. That is why it won't work on Flexreaper. Same as Hulu +. The app was authorized for the A500 HC but not ICS. Your CM9 has a different build.prop and is probably reporting a different device to the app. If you want to use MLB you will have to modify your build.prop to trick the app so it thinks you are on an authorized device.
Evo 4g LTE, Evo 3D, Acer Iconia A500, Samsung Galaxy Tab 2 10.1, Ipad 2, Nabi 2,
Hboot: 1.12 S-Off (Lazy Panda)
MeanBean 3.09 or newer
Firmware: Latest bits installed
Kernel: Mikey's baked in kernel!