So if you get that error, the problem is caused by images not correctly loaded by libjpeg. Try to use default themes clone and check if changing theme works, if so, it's definitely an image loading problem.
Okay, I tried switching between the default and default copy, and the error is the same. I don't need CFW or something for this, right?
I also get an error, a different error, when trying to load the system information app through the shell. I don't know if that's relevant or not.