I also had the same problem and this thread solved it, thanks!
However, a notice: I did not have to set $registerWithJS=1 when using the evaluation copy. After getting the professional version, things stopped working and I was stumped. I'm pretty sure the only thing I did after getting my licence was replacing swf files and clearing my IE cache. I didn't even replace the FusionCharts.js file. Isn't that wierd?