Ajax and IE6 - IE7 runs very very slow... Firefox is fast

Hi guys... i just implementa site that uses ajax update panels.. one page have an ajax update panel with asimple post back data (in change index event of a drop down a record shows tothe user) quite simple!

BUT the problems startswhen i upload the site in a production server , every update panel runs veryvery slow with IE7 or IE6 but in firefox works like a charm..

I made the following changes just to know but NOTHING CHANGED...

<compilation debug="false"><system.web.extensions> <scripting> <scriptResourceHandler enableCompression="true" enableCaching="true"/> </scripting></system.web.extensions> 

i set also the EnableViewState =false to several items inside the page but did'nt see any change in production server..

Help ME PLEASE!!!

hello.

hum...do you have an anti-virus on? are we talking about how much data inside the updatepanel?

no antivirus..

look..

i have an update panel that contains a dropdown box with 3 values

This dropdown is autopostback=true

Also inside the Update panel is a second DropDbox that is conected to a datasource that changes the where clause value from the 1st Ddownbox selected value..(the table contains indexes and there are 80 records ONLY)

is quite simple.. User chooses for example CARS , and the second dropdown manipulates cars brands .. chooses motorbikes ,the second dropdown manipulates bikes..
I do not understand why in firefox is quite fast and in IE7 is VERY very slow...

is it a matter of the production server? or is a general known problem of ajax asp.net with IE6,7?

is there anyone with the same situation?