First of all: a 404 is definitely not nice, but functionally it could just work fine.
It looks like an invalid reference is made, based on the timing I would say: definitely from the same page as your Mendix Charts widget is on. Or is it shown directly when you load the first page?
You could first create an empty homepage to see if it is a specific page or just the complete framework. If the problem only occurs when you load a page, it's probably a widget on that page, then try to remove any widget and see if that also removes the error.
If the problem also occurs when you load an empty page, I would still suspect some widget to cause your issue. Try to remove the .mpk file in your widgets directory when the problem persists (including its usage in your project).
When you have found the widget responsible, check if you can update or replace it.