This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma 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.