While trying to add a MySQL 4.1 database server via Tools & Settings -> Database Servers the following error appears:
Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'USER 'u55excw34eda'@'%' IDENTIFIED BY '<SOME_PASSWORD>'' at line 1
Internal product issue #PPPM-3265
This issue has been fixed in Plesk 12.0.18 MU#64. Make sure that all MU are installed on the server.
Please note: DB management through phpMyAdmin will not function as phpMyAdmin 4.4.9 has no support of MySQL 4.1.