Check the ReleaseNotes.htm file that came with Windows SDK. In section 6.6 it lists the samples that don't compile due to changes in the last CTP of WinFX and in section 6.6.12 is presented exactly this error:
"
6.6.12 Many Windows Presentation Foundation samples do not build
A recent change to the schema location in Windows Presentation Foundation causes many samples to not build. The changes are the following:
1. old = "http://schemas.microsoft.com/winfx/avalon/2005"
new= "http://schemas.microsoft.com/winfx/2006/xaml/presentation"
2. old = "http://schemas.microsoft.com/winfx/xaml/2005"
new = http://schemas.microsoft.com/winfx/2006/xaml"
"