Cannot add device

I was having problems uploading workouts from my Edge 500 using Garmin Express. I tried removing it from Garmin Express and was hoping to re-add it, to see if that would resolve the issue. When trying to add the device, it is correctly detected by Garmin Express, but the following message is displayed: "We're unable to add this device because our servers are unavailable at this time."

I've been through the following steps as suggested by the support page for that message:

• Garmin Express is up to date
  
• Internet connection is a high-speed connection
  
• Computer date and time are correct
  
• There is no outgoing firewall
  
• There is no proxy required
  

I've even tried completely uninstalling and reinstalling Garmin Express, following the appropriate instructions from the relevant support page.

I still get the same message when trying to add my Edge 500.

Do you have any further suggestions?