If you have the problem, that Visual Studio 2010 complains ‘Cannot register duplicate name ‘XXX’ in this scope’, check if you have resources with a x:Name instead of x:Key-Name:
<SolidColorBrush x:Name="NonWorkingResourceName" Color="Red" />
<SolidColorBrush x:Key="WorkingResourceName" Color="Blue" />
Replace x:Name with x:Key and everything is ok.
Read the full post here ...