This project is not associated with an Oracle Service Bus Configuration.

Let's face it, the Eclipse Plugin for OSB in 11g has still some problems.
Closing and opening a Configuration and its Projects doesn't bring you back to the initial state: you get a nice

This project is not associated with an Oracle Service Bus Configuration.

error.

What to do? I have tried several hacks, including restarting Eclipse,
finally the only solution was to create a new configuration and drag the project inside.