Hi Kari-
(I am Kari too. Are you Scandinavian? My father was Norwegian.)
Anyway I found the following in a the November 1996 newsletter from the Palm Beach County
Poultry Fanciers Association. Hope it helps.
Kari S.
http://www.afn.org/~poultry/
"Symptoms of Crop Impaction
Crop Impaction is where the crop of a chicken fills with material that will not pass through the birds digestive system. Most of the time it is caused from eating certain weeds that bulk up when swallowed. A chicken with an impacted crop will stand around, maybe sit on its roost, and look depressed. When you pick it up, the crop may be hard and distended, or liquid and distended. The real clue is that if you hold the mouth open and smell, there's a nasty, sour smell, not the usual chicken breath smell at all.
Chickens often have full crops, but will be active and always ready to eat `one more thing', with no foul odor on their breath. With a lightly impacted crop, sometimes a little mineral oil will lubricate things enough for the mass to pass through. In more severe cases, surgery is required to open the crop and remove its contents."