I have just started working in Eagle and came to the problem above. I had for gotten to add a capacitor and I thought that I could added on the schematic and would move to the board. It is possible that being on the board and reshaping the board dimensions I had deleted one the air connections, I don't know. How do I make the board take the changes on the schematic? I looked on line and people only talks about what it means but not how to solve it.
Thanks