Same issue here in the USA (in California at the moment). Tried to login on Flying Blue and Air France on computer and the App, got the same error message. My guess is that it has something to do with the new month and loading the new promotions. System probably crashed because of people looking for deals OR they loaded some deals wrong (more likely) and shut the system down to fix their error. Sure hope they didn't contract out to BA for technical help.....

Sorry, an unexpected technical error occurred. Please try again or contact Flying Blue customer service.

Now it says:

Sorry, our system fell asleep. Please restart your login.