This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
It looks like Spring is confused and is matching your argument to the constructor that is expecting a Configuration object. It is trying to cast the String to a Configuration and is throwing an exception. Try to explicitly define the type of the argument.
Just some other stuff you might find useful:
I prefer using Java Config I think it is just much easier. Here is an example of that.