In a recent post ("#Apple Airport Extreme due for firmware update? iCloud causing mobile me error to flash on base station?" ) I asked if anyone else was seeing an error on their Apple Airport Router after migrating their Mobile Me account to iCloud.
It appears that I am not alone in discovering that migrating from Mobile Me to iCloud breaks the Back to my Airport feature on Airport Extreme, Express and Time Capsule.
You can flag the error in the Airport Utility application so that the Airport is not constantly flashing an amber light but the point is that Apple should be working on a firmware update for their Airport Routers so that the mac.com or me.com email address and password is recognized.
It may be possible that they can fix this on their server back end by re-directing the routers to an account that will correctly authenticate. The challenge with that is that not everyone has transitioned to iCloud so a simple server redirection in DNS will probably break authentication for people that have not migrated and are still on Mobile Me.