Esellerate servers will still work until September 30th and, all Esellerate serial numbers are already registered to the new system (SORACO), so they can activate there too so, it's not a problem you got an Esellerate Serial Number (the ones that begins with FSDT), since it can be activated on *both* servers until September 30th, and it will always activate and reactivate on Soraco, after Esellerate will close down.
Your problem is that, for some reason ( most likely a firewall ), the software couldn't not connect to Esellerate and couldn't even connect to Soraco so, the "offline" License Wizard from Soraco came up, because it though you had no Internet connection.
And, while an Esellerate Serial Number CAN be activated on Soraco normally when using the Addon Manager, it won't be recognized by the "offline" wizard, because its syntax is not known to Soraco.
So, your real issue is why you couldn't contact both Esellerate (which is still working), nor Soraco servers, and this can only possibly be caused by a firewall which is blocking all outgoing connections to our software, so it's trying to do an offline activation. Disable every kind of firewalls, antivirus, etc, while activating.
And don't worry, you haven't got a "crippled" Serial Number you cannot activate offline in the future, should you need it. When you succeed to activate it online for the first time, you'll get a new Soraco Serial Number too, which CAN be activated by the "offline" wizard. This would be a problem only in this transition but, it shouldn't normally happen, since BOTH Esellerate and Soraco servers are working and both will accept your Serial Number.