I think i am facing the same problem faced by OP in the thread
http://www.fusioncharts.com/forum/Topic1752-37-1.aspx
The solution in his case was to use exact dimensions in width and height in embed tag without px, but the solution doesn't seem to work for me.
Here's the tag I'm using to render the chart
The problem is random with 50% - 75% frequency and I have tested and observed the problem in IE 5 and 6 on atleast 10/12 different windows XP SP2 machines. However the problem doesn't occur in FF, haven't tested on other browsers. I'm useing FC version 3
Please help.
Thanks,
Ashwin