I have a .net application which copies bunch of files to a specific FTP folder on a debian machine on periodical basis, ftp folder has 755 mod, owner of the directory is the ftp username that I authenticate in .net application. So far I tested this application with bunch of debian boxes, my initial attempts generally fail with following message if I try it with a debian machine that I haven't tried it before:

"remote server returned an error 550 File unavailable"

When I see this error, I log onto another debian machine on my network, and I try FTP'ing the debian box that returns the error message from command line. I generally "put" a very small file to the folder in question, right after that windows application starts copying files successfully via FTP. It is as if my command line ftp operation fixes the problem and makes debian compatible with my .net application.

I checked permissions before and after the problem, it doesn't look like what I did changed anything, I am at loss understanding why this problem occurs and why it is fixed with my silly hack.

Can anybody tell me where to look at next to fix this extremely annoying issue?