researching it, it turned out he got a 550 response back from a SIZE command
and then I fell over the text in RFC3659 that says:
The presence of the 550 error response to a SIZE command MUST NOT be taken
by the client as an indication that the file cannot be transferred in the
current MODE and TYPE.
In other words: the change I did on September 30th 2008 and that has been
included in the last two releases were a regression and a bad idea. We MUST
NOT take a 550 response from SIZE as a hint that the file doesn't exist.
gets a 550 response back for the cases where a download (or NOBODY) is
wanted. It still allows a 550 as response if the SIZE is used as part of an
upload process (like if resuming an upload is requested and the file isn't
there before the upload). I also modified the FTP test server and a few test
cases accordingly to match this modified behavior.
