In the mean time I have found a workaround. The cause of my problem appeared to be the following:
1. I instantiate a View via a separate Init process (like in the MEF template projects in Visual Studio)
Public Sub Initialize() Implements IModule.Initialize
_regionManager.RegisterViewWithRegion(strRegionName, Function() _serviceLocator.GetInstance(Of PersonBannerView)())
2. in the XAML code for the View I refer to the ViewModel in order to use it's properties, so the View instantiates it's related ViewModel, without any parameters
3 the constructor of the ViewModel is like I showed in my previous message, so with the IEventAggregator. That constructor does have one parameter, so causes the error message.
Public Sub New(ByVal eventAggregator As IEventAggregator)
m_eventAggregator = eventAggregator
The workaround I have found is that I instantiate the ViewModel from the View's code-behind instead, where it can be done without the parameter-confusion. What I miss in this construction is the advantage of being able to get to the properties of the ViewModel. I
cannot set the ViewModel in the UserControl.Resources and hence not refer to it as a StaticResource. If you have a better suggestion, please come up with it. I keep the feeling that I have lost some advantages of MVVM I used to have before.