I am try to add or remove OccupantsIDs using following methods.
1)Add OccupantsIDs
objChatDialog.pushOccupantsIDs = newAddUserList
    QBRequest.update(objChatDialog, successBlock: { (QBResponse, QBChatDialog) in
    }, errorBlock: { (QBResponse) in
        appDelegate.hideLoader()
    })
2)Remove OccupantsIDs
        objChatDialog.pullOccupantsIDs = leaveGroupID
        QBRequest.update(objChatDialog, successBlock: { (objQBResponse, objQBChatDialog) in
        }, errorBlock: { (objQBResponse) in
        })
While i will use above code some time it will work and some time it will return error 'You don't have appropriate permissions to perform this operation'.
NOTE: i am trying with the group owner user (Which created group dialog).