Try using a different search engine. DuckDuckGo did the 404 for me. Google worked.

 I don't care what they say it's not cookies . Something isn't quite right and the tech that is supposed to work on site is probably going by their own pc . Mines doin same and my pc isn't 2 years old and up to date.

 I too am sick and tired of constantly getting this error even after cleaning out cookies and cache.  Other web sites don't have this bad behavior.

I'm sorry to hear you got this error, @TimoMc. I do not see any reported outages and the website is currently working. Let's try clearing your browser's cookies and cache. Here you'll find the steps if needed: https://aarp.info/2I3wo4C Please let me know if this worked for you. Thank you!