I'm trying to export a set area from a command script.

I currently have:

fw.documents[0].exportTo('file:///C:/test.jpg',{exportFormat:'JPEG',jpegQuality:100});

If i try using:

crop:true,cropBottom:100

in there then I just get an error.
Has anyone got any ideas how to export a selected area, or what I might be doing wrong?

Thanks