First thing to check is if your scenario still works when you remove the new stat. If you continue to get the error, that means you have instructions somewhere that are causing problems.
I would check the "name" for the actual stat, as I didn't see any kind of key sanitization in the source code. If you've added a double-quote in the name for your stat, it might be interfering with some behind-the-scenes code.
Next place to check would be the description for the stat, as well as the ranges. If those are clear, check if you're using the custom stat progression box (the one that lets you add Javascript).
And if all of *that* is good, then you should export your scenario and try it on the desktop version. You would do this by trying to export somewhere like Google Docs so that you can import it from the desktop client.
Beyond that, FieryLion may have more ideas. Those are mine as a web developer. I see this error frequently with my day job when someone doesn't pair quotes or tags correctly.