the system tell me the database has an error and I cant read.

Excepción: lib/dml/simpletest/testdml.php / ► dml_test / ► test_unique_index_collation_trouble
Unexpected exception of type [dml_write_exception] with message [Error al escribir a la base de datos] in [/var/www/ktm/moodle/lib/dml/moodle_database.php line 394]
Debug info:
Duplicate entry 'aäa' for key 'mdl_unittabl_nam_uix'
INSERT INTO mdl_unit_table (name) VALUES
[array (
0 => 'aäa',
)]
line 874 of /lib/dml/mysqli_native_moodle_database.php: call to moodle_database->query_end()
line 916 of /lib/dml/mysqli_native_moodle_database.php: call to mysqli_native_moodle_database->insert_record_raw()
line 2885 of /lib/dml/simpletest/testdml.php: call to mysqli_native_moodle_database->insert_record()
line ... of ...

Fallo: lib/dml/simpletest/testdml.php / ► dml_test / ► test_sql_binary_equal
SQL operator "=" is expected to be accent sensitive at [/var/www/ktm/moodle/lib/dml/simpletest/testdml.php line 2919]
Fallo: lib/dml/simpletest/testdml.php / ► dml_test / ► test_sql_binary_equal
SQL operator "=" is expected to be case sensitive at [/var/www/ktm/moodle/lib/dml/simpletest/testdml.php line 2922]