I am having the same issue, but on all IE versions (currently IE 9 in standards mode). However, I have ensured that I am not using the same ID than the variable name, the code looks like:
<div id="chartdiv1"> </div>
var myChart1 = new FusionCharts("Pie3D.swf", "myChartId1", "500" , "300","0","1");
I'm kind of puzzled because according to your explanation, the problem should be fixed. I have also verified with Firebug that myChart1 is undefined and myChartId1 does not exist right before the chart is created.
Thanks for your help