I see that other people have had this error too but so far no good answers. Maybe my errors will shed new light?

I have just updated an install tried to upload it and right at the end before the renaming, I get Error #0.
I thought maybe a permissions error, so I tried the install for a different app to the same FTP directory. Uploaded perfectly.
Then I went back to the erring install tried again. Still same error.
I tried sending it to a different folder - Error 0
Then to another server - Error 0.
Each of these trials included sending to both ftp.server.com/whereever and www.server.com/wherever
Both servers and all folders tried were able to accept a different install.exe
AND all servers and folders accepted all installs when sent sent using the FireFTP tool in Firefox.

Hope this helps.
Chris C