Thanks, that did the trick. Although that portable library plug-in introduced the following warning in my error list, but it seems to work anyway.
Warning 1 The following exception occurred creating the MEF composition container:
Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.
The default code generator will be used. C:\Program Files (x86)\MSBuild\Microsoft\Silverlight\v5.0\Microsoft.Ria.Client.targets 303 5
Warning 1 The following exception occurred creating the MEF composition container:
Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.
The default code generator will be used. C:\Program Files (x86)\MSBuild\Microsoft\Silverlight\v5.0\Microsoft.Ria.Client.targets 303 5