I encountered this issue, but in my case the password for the 'phpmyadmin' user did not match the contents of /etc/phpmyadmin/config-db.php
Once I updated the password for the 'phpmyadmin' user the error went away.
These are the steps I took:
mysql -uroot -pYOUR_ROOT_PASS
use mysql;
UPDATE mysql.user SET Password=PASSWORD('YOUR_PASS_HERE') WHERE User='phpmyadmin' AND Host='localhost';
FLUSH PRIVILEGES;
DONE!! It worked for me.