What is the file type? It may not be an allowed file type. Also if the file exceeds 1 megabyte, we will not allow it to be uploaded. (You can however host it somewhere else and post the link)
Based upon Nana's other posts about trying to find a way to upload/download large data files... Most likely that was the problem in that he was trying to attach something too big beyond what's stated uder the words Attach file: Maximum size: 1048576 bytes NihabaAshi
May I ask whether ET would run virus checking on each attachment file automatically and immediately after a file's uploading?