Thanks for your answer but the problem is not the configuration.
If I throw the code from a button I download the files work in IE8. But I need to throw in the load event and then does not work in IE8.
Anyway I could fix this by grouping the two reports. Could help me with this issue, I said that I can combine two reports into one report and this could be a solution for me.
I put the link to the topic that I wonder about it.
http://forum.stimulsoft.com/Default.aspx?g=posts&t=4593
Thanks.