AjaxToolKit 4.0 Convert to AjaxToolKit 3.5 error

Hi,

At first,I am using AjaxToolKit 4.0, .NET Framework 4.0 to develop my web site.When come to IIS6, it does not support .Net framework 4,0 and i am not allowed to install .Net framework 4.0 to server. So I have to downgrade it to AjaxToolKit 3.5, .NET Framework 3.5.

I am able to downgrade .NET Framework 4.0 to 3.5 but not able to downgrade AjaxToolKit 4.0 to 3.5.

I have tried to removed the control control i added in toolbox and replaced it with AjaxToolKit 3.5. Remove the AjaxToolKit 4.0 control used in the web page and replaced it with the 3.5 control, but it yet prompt me the error.

Can some one help? Please.....