Robust FTP control for D7

We have been using native windows FTP calls to handle our FTP needs in D7
service apps.
But we have several clients for whom the up and download process fails. We
have spent man-months of time trying to find the problem w/o success. So am
looking for a very robust 3rd party tool to handle all our FTP needs. If it
matters, the app that mainly uses the FTP functions is running as a service.


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