Ok, I thought our tests could be faster, but I will give you some manual what to check:
1. There is probably bug in:
administrator/components/com_artiofusioncharts/views/artiofusionchart/tmpl/form_source.php - around line 31
should be this row:
$document->addScriptDeclaration('window.addEvent(\'domready\', function() { ARTIOFusionCharts.fillSource("' . $this->escape($importSource) . '"); } );');
modify it to:
$document->addScriptDeclaration('window.parent.addEvent(\'domready\', function() { ARTIOFusionCharts.fillSource("' . $this->escape($importSource) . '"); } );');
Check if it help you, but I think it will not, because you have there some problems I could not simulated.
2. If it doesn't work, check this file:
administrator/components/com_artiofusioncharts/helpers/helper.php - around line 1029 as warning message show you.
Write there before this row this code:
var_dump(FILEINFO_MIME_TYPE); die;
If you start to import your file, it should show you what FILEINFO_MIME_TYPE return. It should be something like int(16) as in my tests. If it is not number, let us know about result.