Eclipse custom message unresolved inclusion

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Hello everybody, I know that might be a common question, but all the solutions I have found did not work. I can import my project (around 35 packages) and all the inclusions work perfectly. However, when comes to the inclusion of messages it shows an error and says that the inclusion of the message header is unresolved even if the message is defined in the same package where it is used. Moreover, it builds the project without any problem. Of course I followed the steps in the wiki to set up Eclipse with ROS and catkin. Any clues on what it can be?

Thank you very much

Andrea