I'm trying to display a window as a sheet after a drag operation onto my main window. I'm not sure what the problem is, but the error 'Modal session requires modal window' makes me think that calling a method in another class to call the sheet from the dragOperationConclusion method is a bad idea (i.e the operation hasn't concluded, therefore it's not modal and can't display a sheet. But then, how do you get it to display a sheet if you can't call out from the conclusion method?). I am writing this using cocoa-java, but I have no problem accepting code in the form of ObjC for me to translate. Thanks.