This is a shame! The same thing happened to the Bwin CEOs last year; they also got arrested while negotiating some deals in France. Later they claimed that French police threated them like they were some hardcore criminals.
However, the EU is clearly saying that companies that are licensed in ANY EU country have the right to provide their service in ANY other country within the EU. Still, particularly the French and the German government try to protect the government monopoly on gambling with any means, claiming that private providers are not doing enough to protect players from compulsive gambling.