Cannot specify both Name and x:Name attributes
I think this is a bug in Beta 2, where you can't set x:Name for a UserControl, and then in the parent XAML that uses the UserControl, use x:Name again.
The trick is to remove the name from the XAML for the UserControl - you can use this in the code behind anyway to self reference the user control, so the name here isn't that important.
Update project references
Old SilverLight 2 Beta 1 projects still had references to version 2.0.3xx, some manual add/remove references was required to get the project all happily working on v2.0.50727
That was all the changes I had to do. I think I escaped lightly this time. Oh the joy of playing with beta software.