Double check to make sure you have the correct row number in the Pediaicons.txt file for that particular building. The best way to figure that out is to get the number of the building immediately proceeding it and add 1 to it. If that doesn't work, try incrementing the number by one, and try it to see if it works. If it doesn't repeat the proceeding step until it does.
If that doesn't work, I don't know what will, since that particular process worked with my mods when I had trouble.
EDIT: I just took another look at the screenshot of your civilopedia icons, and noticed what was wrong. The icon for the park is in the row immediatley below that of the knights templar. In the civilopedia.txt file, the knights templar is listed as icon row# 81, and you have the part listed as icon row# 83, when it should be 82, since it is 1 row below the knights templar.
I can pretty much guarantee that that will fix your problem.
