Why NVENC doesn't work if the height is greater than 1080?

I’m using NVENC example provided with NVENC SDK.

I just downloaded NVENC SDK and it has sample called nvEncodeApp. This sample reads YUV from file and provide it as input to nvenc. I need to compress RGB images (1620x1220). I modified the sample that comes wit NVENC SDK so it would convert RGB to YUV and then supply it as input to nvenc. The problem is that it doesn’t work. But, If use RGB images with HEIGHT less or equal to 1080 it does work. But, according to specs it should support up to 4096x4096. What I’m missing?

The image of the spces is here:
https://drive.google.com/file/d/0B_j2rCBlhOaNZlBJRUxlMzhlMWs/edit?usp=sharing

Why it doesn’t work if the height is greater than 1080?