It's always the same reason: Your existing revolve feature is done as a surface. So you can't remove material from a surface with a solid cut.
More interesting is the question: Why is your revolve feature a surface? It's because the sketch for your revolve feature has an open loop. It's pretty easy to see, because there are red points in your sketch (open ends) and the loop isn't shaded. If loops aren't closed, nearly every feature in PTC Creo makes a surface. So just close your loop and change your revolve feature back to solid creation (don't know how it's called, take a look at the picture, please).
English is not my native language 
