I had the same issue with one of my young pullets. I found her sitting quietly, in an unusual location, by herself while the girls were out free ranging in the yard. I picked her up and noticed her crop was mushy (like a deflated balloon). I actually ended up helping her vomit, what was left, up. I had to hold her head down, away from me. I gave her drips of water by straw in between vomiting. I ended up sleeping with her on the couch that night and then fed her plain yogurt and some scrambled egg the morning. She seemed alot better so I slowly added some of her regular food to the yogurt until she was eating normal again. I haven't had any problems so far but I am still keeping an eye on her for the same reasons that MarieNC was talking about. I hope it doesn't become a chronic thing. I thought maybe my girl had sour crop or just ate something icky.
Good luck with your roo! Keep us posted!
Good luck with your roo! Keep us posted!