My MySQL server sometimes refuses queries and returns the message 'Errorcode: 13'. What does this mean? ¶

This can happen due to a MySQL bug when having database / table names with upper case characters although lower_case_table_names is set to 1. To fix this, turn off this directive, convert all database and table names to lower case and turn it on again. Alternatively, there's a bug-fix available starting with MySQL 3.23.56 / 4.0.11-gamma.