If you are getting the "user does not exist" message recently (if the user icon is not green; this only applies to M121S and TVpad 2 users with firmware 3.0 or higher), then read further.
I believe there were some problems with the authentication server of the TVpad (causing the "user does not exist" message). I have read that it should be fixed now. Also, try to restart your TVpad (try several times if needed) if you are getting the user does not exist message, this may help. If you are still getting the "user does not exist" message after restarting and this problem is taking longer than 1 day, contact the customer service on the official site about your problem and include your MAC address of your device (this can be found beneath your device).
The servers should have been restored now. If you still get the user does not exist message, please contact the customer service. You can also try to change the DNS number if you still get the user does not exist message, see this post: how to fix user does not exist message