We don't, at this time have definitive information from users who are able to run complex network diagnostics, but preliminary information gives the appearance that Orange has different policies for Second Life network traffic, and that this may have overloaded or gone awry.
Some ISPs or ICPs apply differing policies to different kinds of network traffic or traffic going to different network destinations, often limiting data flows by slowing down packet rates (increasing lag) or dropping packets (increasing packet loss) to force lower data throughputs. The opposite of this practice is called Network Neutrality.
Often the process is difficult to detect, unless it goes wrong or overloads. It is, however, possible that the problem has been caused by another issue such as BGP route flapping though the anecdotal evidence we have received would seem to indicate otherwise, as the symptoms (as reported) seem to be what you'd expect if large numbers of Euro users attempted to connect to Second Life, and far exceeded a bandwidth restriction policy.
One question that comes to mind is why would Orange host an event in Second Life while also restricting traffic to Second Life? Well, the divisions involved in each part are definitely distinct. It may be that neither one has ever had any reason to communicate with the other. It may be that they may not even technically be a part of the same company - it isn't uncommon for several companies providing groupable services to operate under an umbrella name, even though they may not have any corporate structure or management in common.
We contacted Orange through Metaversatility for comment and additional information, but as it is Saturday in France, we are not expecting to receive a rapid response.