(Your message was marked as spam in my gmail, so I didn't see it until now. Not sure why, but probably because of the links. Perhaps this is related to why the group was blocked for a few days. Not your fault, of course.)
There is no string in the Google Charts code matching what you are seeing "Potential error in stylesheet ...", but I would suspect the error relates to the stylesheet it is referring to: "themes/xenea/style.css", and how that might be applied to the chart. In that page that shows the error, I see: "<link rel="stylesheet" href="themes/xenea/style.css" type="text/css" media="all">" So you should probably investigate where that is coming from.