Hi Andrea,
The payload too big is EXCLUSIVELY a websockets error. So in your case, websockets are still being used. Maybe your presence.js file was cached somehow. The solution is NOT to use websockets or upgrade to 2.27. If your code is older than a year, then the upgrade has a cost, maybe that is why it is not taking your code? What is the exact message you get when trying to upgrade, does it say EXPIRED? If you try to reuse the code without an upgrade or with the old version running, then it will say that the code is not available. In any case, the payload error happens ONLY when websockets are in use, there is no payload limitations in flash xmlsockets, so be sure it is disable if you are unable to upgrade FOP to version 2.27