Error message:

APPLICATION ERROR # 401
Database query failed. Error received from database was #1066: Not unique table/alias: 'mantis_custom_field_string_table' for the query: ..."

Here is a sample broken query:

SELECT Count( DISTINCT mantis_bug_table.id ) as idcnt FROM mantis_bug_table JOIN mantis_project_table ON mantis_project_table.id = mantis_bug_table.project_id LEFT JOIN mantis_custom_field_string_table mantis_custom_field_string_table_12 ON mantis_bug_table.id = mantis_custom_field_string_table_12.bug_id AND mantis_custom_field_string_table_12.field_id = 12 LEFT JOIN mantis_custom_field_string_table mantis_custom_field_string_table_5 ON mantis_bug_table.id = mantis_custom_field_string_table_5.bug_id AND mantis_custom_field_string_table_5.field_id = 5 LEFT JOIN mantis_custom_field_string_table mantis_custom_field_string_table_3 ON mantis_bug_table.id = mantis_custom_field_string_table_3.bug_id AND mantis_custom_field_string_table_3.field_id = 3 LEFT JOIN mantis_custom_field_string_table mantis_custom_field_string_table_2 ON mantis_bug_table.id = mantis_custom_field_string_table_2.bug_id AND mantis_custom_field_string_table_2.field_id = 2 LEFT JOIN mantis_custom_field_string_table mantis_custom_field_string_table_13 ON mantis_bug_table.id = mantis_custom_field_string_table_13.bug_id AND mantis_custom_field_string_table_13.field_id = 13 LEFT JOIN mantis_custom_field_string_table mantis_custom_field_string_table_14 ON
mantis_bug_table.id = mantis_custom_field_string_table_14.bug_id AND mantis_custom_field_string_table_14.field_id = 14 LEFT JOIN mantis_custom_field_string_table mantis_custom_field_string_table_5 ON
mantis_bug_table.id = mantis_custom_field_string_table_5.bug_id AND mantis_custom_field_string_table_5.field_id = 5 WHERE mantis_project_table.enabled = ? AND ( mantis_bug_table.project_id = 22 ) AND ( ( mantis_bug_table.status in (?, ?, ?, ?, ?, ?) ) AND (mantis_custom_field_string_table_12.value = ?) AND ((mantis_custom_field_string_table_5.value LIKE ?)) AND (mantis_custom_field_string_table_3.value = ?) AND (mantis_custom_field_string_table_2.value = ?) AND (mantis_custom_field_string_table_13.value = ?) )

The tablename_id is used for aliasing, such table names are not expected.

I suspect that mantis_custom_field_string_table_5 is the cause of the issue, since it is referenced twice.

I've revised the issue title and description to reflect the root cause. I'll submit a pull request shortly.

Here is the pull request:
https://github.com/mantisbt/mantisbt/pull/602