When the field "task" of the form is set to "not visible" in the "Screen customization > Ticket", the ticket cannot be updated > a red block says we must look at the log file :

For exemple:

2017-12-15 10:18:21.396 ** ERROR ** [V6.4.3] Exception-[23000] SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'Ticket-2370' for key 'workelementReference'
2017-12-15 10:18:21.399 ** ERROR ** [V6.4.3] For query : insert into workelement ( refType , refId , idActivity , idProject , refName , realCost , idUser , ongoing , done , idle ) values ('Ticket', '2370', '2450', '352', '[tests] Page “Ajouter une séance”', '4409738.09', '144', '0', '0', '0')
2017-12-15 10:18:21.403 ** ERROR ** [V6.4.3] Strack trace :
2017-12-15 10:18:21.406 ** ERROR ** [V6.4.3] #0 Sql->query called at [C:wampwwwprojeqtormodelpersistenceSqlElement.php:1120]
2017-12-15 10:18:21.410 ** ERROR ** [V6.4.3] #1 SqlElement->insertSqlElement called at [C:wampwwwprojeqtormodelpersistenceSqlElement.php:929]
2017-12-15 10:18:21.413 ** ERROR ** [V6.4.3] #2 SqlElement->saveSqlElement called at [C:wampwwwprojeqtormodelpersistenceSqlElement.php:619]
2017-12-15 10:18:21.416 ** ERROR ** [V6.4.3] #3 SqlElement->save called at [C:wampwwwprojeqtormodelWorkElementMain.php:177]
2017-12-15 10:18:21.420 ** ERROR ** [V6.4.3] #4 WorkElementMain->save called at [C:wampwwwprojeqtormodelWorkElementMain.php:322]
2017-12-15 10:18:21.424 ** ERROR ** [V6.4.3] #5 WorkElementMain->save called at [C:wampwwwprojeqtormodelpersistenceSqlElement.php:1529]
2017-12-15 10:18:21.427 ** ERROR ** [V6.4.3] #6 SqlElement->saveDependantObjects called at [C:wampwwwprojeqtormodelpersistenceSqlElement.php:1467]
2017-12-15 10:18:21.430 ** ERROR ** [V6.4.3] #7 SqlElement->updateSqlElement called at [C:wampwwwprojeqtormodelpersistenceSqlElement.php:923]
2017-12-15 10:18:21.434 ** ERROR ** [V6.4.3] #8 SqlElement->saveSqlElement called at [C:wampwwwprojeqtormodelpersistenceSqlElement.php:619]
2017-12-15 10:18:21.437 ** ERROR ** [V6.4.3] #9 SqlElement->save called at [C:wampwwwprojeqtormodelTicketMain.php:390]
2017-12-15 10:18:21.441 ** ERROR ** [V6.4.3] #10 TicketMain->save called at [C:wampwwwprojeqtortoolsaveObject.php:78]