For the last 10 days, I've had adhoc 'duplicate upload file error's again, 24 of them.
They only occur after three consecutive attempts at inserting a duplicate record into the database, that is one where the time in the modem file you upload, which is always a whole date/time minute with no seconds, already exists in the database. This can be caused by all sorts of things, usually running two instances of an upload program at once or having a clock that's suddenly lost or gained time. There is no easy way round this but 99.9% of the time there is no problem.
In your case, it's a bug because you are uploading almost exactly on the minute but varying by a few secs due to the time you take to process the data and rounding to the nearest sec at the server is causing the duplicates. If you stop DSLstats for 10 secs and restart it should stop this.
In theory you can have 1440 a day. I banned someone 4 months ago who had managed 5000 bum uploads consecutively - and they were
still sending them but e-mail is invalid. Still have to be processed though, so blocked the IP.