Getting 404 trying to create group collaboration on a folder via Java SDK

Hello,

I'm using the Java SDK to create a collaboration on a folder for a group.  Both folder and group were created by the AppUser.  I get

 "The API returned an error code: 404"

trying to do this:

BoxCollaboration.Info collabInfo = collabFolder.collaborate(collaborator, BoxCollaboration.Role.EDITOR);  

where

BoxFolder collabFolder =  getBoxFolderByName(BoxFolder.getRootFolder(appUserCon), folderName);
BoxGroup collaborator = getBoxGroupByName(appEntCon, groupName);

Note that I'm using AppEnterpriseConnection to get BoxGroup and AppUserConnection to get BoxFolder, as that seems to be the only way I can get those objects. 

What am I doing wrong?  If anyone has succeeded in adding collaborations via API, can you share your experience?

Thanks,

Kumi