How to fix: The widget settings is not valid. Page title is invalid.
If your menu items use special or accented characters — like à, í, ê, —, or anything that’s not your everyday A to Z — you’re probably running into a character encoding issue. But no worries, this one's easy to fix. Here’s how:
Go to the Layout tab. Find the Page List gadget (that’s your navigation menu) and hit the ✏️ pencil icon. That’ll open up the settings popup.
Clean up your labels. In the gadget config window, check your gadget title, page names, and URLs. Replace any special or accented characters with standard ones — just plain old Latin characters (A-Z, no frills).
Avoid things like:
à,ê, or encoded characters like\xe0,\xf9. These often break things when the theme reloads or when editing raw code.If those characters are also part of the actual Page URLs, you’ll need to update them too — go to Pages > Edit, and adjust the URL slug manually.
Page List gadget configuration window
That’s it! Just keeping your navigation clean and simple can save you a lot of theme headaches down the road.
Reference:
Blogger support forum: The widget settings in widget with id PageList1 is not valid. Page title is invalid.