phpMyadmin told me today:

Connection for controluser as defined in your configuration failed

Luckily I came across a helpful post telling me to change:

$cfg['Servers'][$i]['controluser'] = 'pma'; $cfg['Servers'][$i]['controlpass'] = 'pmapass';

to:

$cfg['Servers'][$i]['controluser'] = ''; $cfg['Servers'][$i]['controlpass'] = '';

....and the error was gone :-)