After making a nice project prototype you feel the need to use in a real deployment then follow the following steps.
back up your project
In the Projects panel, right-click the top project folder (e.g. SilverlightPrototype1), and then click Open Folder in Windows Explorer.
In Windows Explorer, right-click the .csproj file (for example, SilverlightPrototype1.csproj), click Open With, and then click Notepad++ or scite.
In the text file, locate and then delete the following two lines (capability flags):
<ExpressionBlendPrototypingEnabled>false</ExpressionBlendPrototypingEnabled>
<ExpressionBlendPrototypeHarness>true</ExpressionBlendPrototypeHarness>
Save and close the text file. When prompted to reload the project file, click Yes.
In the References folder, locate and right-click Microsoft.Expression.Prototyping.Runtime.dll, and then click Remove from Project.
Right-click the top project folder again, and then click Add Reference. In the Add Reference dialog box, browse to the Microsoft Silverlight SDK, and then locate and click the System.Windows.Controls.Navigation.dll. The default location is C:\Program Files\Microsoft SDKs\Silverlight\v3.0\Libraries\Client.
Click Open.
In the Projects panel, right-click the next project folder (for example, SilverlightPrototype1Screens), and then click Open Folder in Windows Explorer.
In Windows Explorer, right-click the .csproj file (for example, SilverlightPrototype1Screens.csproj), click Open With, and then click Notepad.
In the text file, locate and then delete the following two lines (capability flags):
<ExpressionBlendPrototypingEnabled>false</ExpressionBlendPrototypingEnabled>
<ExpressionBlendPrototypeHarness>true</ExpressionBlendPrototypeHarness>
Save and close the text file.
In the References folder, locate and right-click Microsoft.Expression.Prototyping.Runtime.dll, and then click Remove from Project.
In the top project folder, expand the App.xaml node, and then double-click App.xaml.cs to open the file.
In the App.xaml.cs file, locate the following code:
[assembly: Microsoft.Expression.Prototyping.Services.SketchFlowLibraries("MyProject.Screens")]
Note the name of the screens assembly for your project, which appears in place of MyProject.Screens in the code
Read more: http://erew.org/?p=624