If you are running the 64-bit version, try using the 32-bit version instead. If that still doesn't work, contact us.
It is because the game is reading incorrect terrain data that was left over from an old version of the game.
Go to the location where you installed the game, delete the “Oh So Hero_Data” folder, and then re-install.
This will not reset your game progress. Your save data is stored in a different location on your machine (see below) and will not be removed as a result of this.
At your Desktop, press Windows+R on your keyboard to open the Run window.
Next, copy and paste the following line into the Open textbox and click OK:
%USERPROFILE%\AppData\LocalLow\Full Frontal Frog\Oh So Hero
An Explorer window will appear to show you the contents.