Try visiting the modelPanel demo page using IE6, if you can see the close button there, that means you have an error in your code
Thanks for you answer.
I tried this modalPanel demo, result:
example 1: OK
example 2: KO
That means the problem is when we call modalPanel using JS way, in IE6 we don't have the close button.
sorry.... I was wrong.. the example 2 doesn't have a close button as control.