placeFiles.file Error 1230 file folder expected

I'm not sure what I'm doing wrong with this.  According to the documentation this should work no?

var placeFiles = aDoc.placedItems.add();

placeFiles.file = ("/Users/ohms/Dropbox/printing/file.ai");

I've also tried:

placeFiles.file = "/Users/ohms/Dropbox/printing/file.ai";

Both of these produce

Error 1230:File/Folder expected

Line: 26

placeFiles.file = same file path as above

I've seen a few suggestion on these errors but don't seem to be able to get it right on mine.