I do not know why but it seems like every version of the Windows Forms control only works with one version of the server. no backward compatibility. and to make it worse .net 4.0 / VS 2010 will not even allow use of the older controls if you need to connect to an older report server!
what i had to do the other day after much trial and error is create a dll that uses the old control and the 3.5 framework and then call that dll from a framework V4 app.
i had to use VS 2008 to even create the dll project!
I know they want us to upgrade but this is nuts!!! yet another thing that is making me have more questions about the use of MS tools and Tech .... MS wake up and see that you are losing developers and customers the more you do this.