Very little info code shown in a picture this is at best hard to see no mention of what platform you are on.
In the picture were half most of your code is blocked from vision.
With no actual question in words.
Ill give you the benifit of the doubt and believe you are actually asking for help instead of just implying that get data is broken on a random ? platform.
You have heightmapcolors = new Color[width * height
Just above that you are loading a heightMap texture in the parameter.
It seems to me the first red flag here is that you are not calling.
heightmapcolors = new Color[heightMap.Width * heightMap.Height]
My bet is on the guess that you have messed up those values for width and height that you are using elsewere and they don't match what get data see's.