Problems with ReportViewer, ScriptManager, and ICallbackEventHandler

I am having problems porting a screen from 32 bit (SQL 2005, WinServer 2003, IIS 6) to 64 bit (SQL 2008, WinServer 2008, IIS 7.5).  This screen uses BOTH iCallBackEventHandler and a Reportviewer object, and works fine on the old server.  (I also had to add a ScriptManager object which was not needed before.)

On the new server, when I issue a SetParameters call, it kills the ICallBackEventHandler interface.  All I have to do is comment out that line, and the program works (but parameters have to be set manually).  Enable it, and my client browser will no longer receive any events sent through the ICallBackEventHandler interface.

Is there any fix for this?  Any way to see what is going on?  Or did we paint ourselves into a corner by using MS products before their architecture was refined enough (I imagine it's going to be a while before we go 128 bit OS)?