I contacted the site owner and this was her response
"It it likely a local storage conflict...I have had 2 folks let me know that they are not able to create a list at work and it is b/c their settings are such that they don't have local storage. My tech gal said it is similar to cookies but a newer technology.
I wish that I could help but honestly I have no idea how it all works. Basically the info is saved on the user side ...so if you have any programs or network restrictions it may not work on your computer. I think most up to date browsers support local storage.
Based on the site here: http://dev-test.nemikor.com/web-storage/support-test/
It looks like there are very few (out of date browsers) which do not support local storage. If you are up to date that should not be the issue.
I hope that helps...also, when using the shopping list for the first time...give it a few seconds to build the list. Sometimes it can take a couple of seconds. Mine always seems to be a bit slower right after I have done any system updates on my computer."
I updated my Google Chrome, Firefox and IE browsers to latest as well as Java. I googled the error but it is WAY above my head - I don't know a thing about writing code etc.
Browser (if necessary): Chrome
updated, googled etc