That error shows up before you click on a portrait, it's because of how I'm creating the "Random Portrait" button. It has no impact on anything. Game still works. The error doesn't show up when you click on portrait, it shows up the first time you click on a slave and view the Customization tab.
Portrait button still works fine for me too. Checked on a fresh install. If you have a lot of portraits, it can take a long time for the window to finish loading. If you don't have enough memory, it could crash the game.