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How does ACEftp differ? That's a good question. You'd have to ask the programmer, cause I've never used it. Perhaps ACEftp autodetects the settings on the server side and switches to the proper transfer mode (PASV or PORT) automatically. Where in with SmartFTP you have to change it manually. That's just a guess and a far-fetched one at that.

There could be many differences within the software which allows it to work better, very hard to say.