The extension I try to upload is Minimeter, its GUID is 08ab63e1-c4bc-4fb7-a0b2-55373b596eb7 I found that the extension adslMeter 1.5, in the sandbox, has the same GUID. In fact, the Developer Comments are "here Minimeter 1.5 for firefox 1.5". https://addons.mozilla.org/en-US/firefox/addon/1652 Since the user SERIFOX hides his address I can't get in touch with him. So I don't know what I'm supposed to do. I'm the developer of Minimeter, which was created by Tom Germeau then developed by me with his agreement. By the way, it would be nice to get a more descriptive message when this error occurs. Including the name of the existing add-on with the same GUID.
Thomas -- seems like you're the author here, re-open this if it's still an issue.