I update the dll of uploadhandler of version 2016.Q2. I find a bug of the handler. if I add the code blew in the UploadHandler.ashx. When I upload file, the upload_FileUploaded event can not be hitted. and the upload_FileUploadFailed event be hitted. and not error message. and the file upload to the server successful. So I use the dll of 2014, it is OK.
public override Dictionary<string, object> GetAssociatedData()
Dictionary<string, object> dict = base.GetAssociatedData();