New users not working on MySQL 5.6 in Amazon RDS

Question

I'm using the CREATE USER and GRANT commands as mentioned here http://dev.n0ise.net/2012/09/amazon-rds-mysql-add-additional-users-with-limited-previledges/

When I try to connect I get this in MySQL Quer Browser:

Could not connect to host '...sa-east-1.rds.amazonaws.com'.
MySQL Error Nr. 0

Output in MySQL Workbench:

Your connection attempt failed for user 'site' from your host to server at ...sa-east-1.rds.amazonaws.com:3306:
  MySQL server has gone away

Some details:

• MySQL version: 5.6.13

• Credentials are typed correctly. When I miss them I get the standard 1045 access denied error.

• The user created with the instance and another limited user I created some weeks ago are working fine

• Same commands worked fine on a non RDS server

Any ideas?

Thanks in advance.