Problems With Uploading To FTP

I have uploaded things to Moon's FTP with no problems in the past, but recently have been having issues. An upload will make it to maybe 20-30%, and then start writing over the file from the beginning again, like it had just started. This makes it impossible to resume uploads, because it seems to drop back to the beginning randomly, and because it always thinks it's starting from 0%. I have tried using several different FTP clients, and they all have this problem, so that is not the issue.

I am on an Intel Mac running MacOS 10.5.2 and use Captain FTP v. 4.3051.

If anyone could point me in a direction to fix this, that would be wonderful.

Jam it back in, in the dark.