Quick PSA to everyone who’s been getting game-breaking bugs about “achievements not declared in startup” or missing variables…the source of these bugs, as far as we can tell, is a cookie that cogdemos tried to use to keep track of where you were in the game between browser sessions, but caused all kinds of problems when the game files were updated.
Cogdemos no longer uses that cookie, but it may still be on your computer and causing crashes. Clearing your cookies and cache should get rid of the problem and let you play through the whole demo without interruption. (If deleting all cookies doesn’t solve the problem, please let us know.)