Maybe this error occurs when you run a program using the Canvas library (used from Unit 2 onwards) more than once. This is a known problem with Canvas, and is not caused by your programming. The only solution is to close all Python windows then re-run IDLE after each time you run your program.
http://level1wiki.wikidot.com/errormessages
Woah thank you! I have already installed hiyacfw by borrowing a friend's computed as I figured out the problem was on my laptop, not the program itself, but its nice to know the exact issue anyway, i'll try this.