The user profile Service failed the logon

Dear all ,
my RDS server 2008 R2 I receive this error "The user profile Service failed the logon" . I use 10 of 16 GB RAM on server.

I see in perfmon the the registry quota is 40 % when I have no users connected on the server. I have a other server RDS a same configuration software and hardware and we have 40 % or 50 % in the registry quota when I have 40 users are connected.

Do you have an idea?

Thanks.