Using of Content Attribute inside a UserControl does't allow me to give namesto child elements

Hey,

i have developed a UserControl which owns a ContentAttribut, which themselfs takes a Grid as only ChildElement.

So far so god, but know, in my MainApplication, in there i implement the usercontrol, if i add the grid i cannot set a name for it, following exception was thrown:

Error    1    Cannot set Name attribute value 'grid' on element 'Grid'. 'Grid' is under the scope of element 'SizeMoveWindowControl', which already had a name registered when it was defined in another scope. Line 9 Position 10.    D:\Programmieren\WPF-Development\Projekte\NetMediaPlayer\NetMediaPlayer\MainWindow.xaml    9    10    NetMediaPlayer

Did anybody has experiences with this issue????