Redmine

That seems to the database config, which is in /your/redmine_dir/conf/database.yml.

I solved the problem. The error was generated by a trigger associated with the table "ISSUES". This trigger is standard, or somebody that was created in our system?

Here is the code:

-- Trigger DDL Statements
DELIMITER $$

USE `redmine`$$

CREATE
DEFINER=`redmine`@`localhost`  <--------------- The problem is here and
TRIGGER `redmine`.`beforeInsertIssue`
BEFORE INSERT ON `redmine`.`issues`
FOR EACH ROW
BEGIN  
    IF NEW.status_id = 1 THEN
        SET NEW.start_date = null;
    END IF;
  END$$

CREATE
DEFINER=`redmine`@`localhost`  <------------------ here.
TRIGGER `redmine`.`beforeUpdateIssue`
BEFORE UPDATE ON `redmine`.`issues`
FOR EACH ROW
BEGIN  
  IF NEW.status_id = 1 THEN
      SET NEW.start_date = null;
  END IF;

  IF OLD.due_date IS NOT NULL AND NEW.due_date <> OLD.due_date THEN
      IF exists (SELECT * FROM custom_values WHERE customized_id = NEW.id AND custom_field_id = 13 AND customized_type = 'Issue' ) THEN
     UPDATE custom_values set value = NEW.due_date WHERE customized_id = NEW.id AND custom_field_id = 13 AND customized_type = 'Issue'; 
      ELSE
         INSERT INTO custom_values (customized_type,customized_id,custom_field_id,value) VALUES ('Issue',NEW.id,13,NEW.due_date);
      END IF;        
      SET NEW.due_date = OLD.due_date;
  END IF; 
END$$

Redmine uses databases only as a "CRUD datastore", i.e. doesn't meddle with triggers or whatever, not even foreign constraints or similar, so it's something someone did at your place.