Thanks for your answer.
Here is a log of the test I have just done
====================================
Log started, 28/10/2013 09:55:43
====================================
SELECT `id`,`start_date`,`end_date`,`text`,`duration`,`progress`,`sortorder`,`owner`,`conge`,`parent` FROM gantt_tasks ORDER BY sortorder
SELECT `id`,`source`,`target`,`type` FROM gantt_links
Done in 0.031241893768311s
====================================
Log started, 28/10/2013 09:55:47
====================================
DataProcessor object initialized
1382954147351_text => Activité
1382954147351_start_date => 2013-10-15 01:00:00
1382954147351_duration => 4
1382954147351_progress => 0.25
1382954147351_parent => 89
1382954147351_id => 1382954147351
1382954147351_end_date => 2013-10-19 01:00:00
1382954147351_!nativeeditor_status => inserted
ids => 1382954147351
Row data [1382954147351]
text => Activité
start_date => 2013-10-15 01:00:00
duration => 4
progress => 0.25
parent => 89
id => 1382954147351
end_date => 2013-10-19 01:00:00
!nativeeditor_status => inserted
Incorrect field name used: sortorder
data
text => Activité
start_date => 2013-10-15 01:00:00
duration => 4
progress => 0.25
parent => 89
id => 1382954147351
end_date => 2013-10-19 01:00:00
!nativeeditor_status => inserted
Incorrect field name used: sortorder
data
text => Activité
start_date => 2013-10-15 01:00:00
duration => 4
progress => 0.25
parent => 89
id => 1382954147351
end_date => 2013-10-19 01:00:00
!nativeeditor_status => inserted
Incorrect field name used: owner
data
text => Activité
start_date => 2013-10-15 01:00:00
duration => 4
progress => 0.25
parent => 89
id => 1382954147351
end_date => 2013-10-19 01:00:00
!nativeeditor_status => inserted
Incorrect field name used: owner
data
text => Activité
start_date => 2013-10-15 01:00:00
duration => 4
progress => 0.25
parent => 89
id => 1382954147351
end_date => 2013-10-19 01:00:00
!nativeeditor_status => inserted
Incorrect field name used: conge
data
text => Activité
start_date => 2013-10-15 01:00:00
duration => 4
progress => 0.25
parent => 89
id => 1382954147351
end_date => 2013-10-19 01:00:00
!nativeeditor_status => inserted
Incorrect field name used: conge
data
text => Activité
start_date => 2013-10-15 01:00:00
duration => 4
progress => 0.25
parent => 89
id => 1382954147351
end_date => 2013-10-19 01:00:00
!nativeeditor_status => inserted
INSERT INTO gantt_tasks(`start_date`,`end_date`,`text`,`duration`,`progress`,`sortorder`,`owner`,`conge`,`parent`) VALUES ('2013-10-15 01:00:00','2013-10-19 01:00:00','Activité','4','0.25','','','','89')
SELECT MAX(sortorder) as maxvalue FROM gantt_tasks
exception 'Exception' with message 'MySQL operation failed
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'maxvalue FROM gantt_tasks' at line 1' in E:\wamp\www\gantt\codebase\connector\db_common.php:1085
Stack trace:
#0 E:\wamp\www\gantt\codebase\connector\db_common.php(747): MySQLDBDataWrapper->query('SELECT MAX(sort...')
#1 E:\wamp\www\gantt\codebase\connector\db_common.php(659): DBDataWrapper->queryOne('SELECT MAX(sort...')
#2 E:\wamp\www\gantt\codebase\connector\dataprocessor.php(170): DBDataWrapper->new_record_order(Object(DataAction), Object(DataRequestConfig))
#3 E:\wamp\www\gantt\codebase\connector\dataprocessor.php(97): DataProcessor->inner_process(Object(DataAction))
#4 E:\wamp\www\gantt\codebase\connector\base_connector.php(491): DataProcessor->process(Object(DataConfig), Object(DataRequestConfig))
#5 E:\wamp\www\gantt\codebase\connector\gantt_connector.php(128): Connector->render()
#6 E:\wamp\www\gantt\codebase\connector\base_connector.php(410): GanttConnector->render()
#7 E:\wamp\www\gantt\samples\common\connector.php(10): Connector->render_table('gantt_tasks', 'id', 'start_date,end_...', '')
#8 {main}
Edit operation finished
0 => action:error; sid:1382954147351; tid:91;
Done in 0.062484979629517s
====================================
Log started, 28/10/2013 09:56:13
====================================
DataProcessor object initialized
1382954147351_text => test with branch ordering
1382954147351_start_date => 2013-10-15 01:00:00
1382954147351_duration => 4
1382954147351_progress => 0.25
1382954147351_parent => 89
1382954147351_id => 1382954147351
1382954147351_end_date => 2013-10-19 01:00:00
1382954147351_owner => 0
1382954147351_conge => 0
1382954147351_!nativeeditor_status => inserted
ids => 1382954147351
Row data [1382954147351]
text => test with branch ordering
start_date => 2013-10-15 01:00:00
duration => 4
progress => 0.25
parent => 89
id => 1382954147351
end_date => 2013-10-19 01:00:00
owner => 0
conge => 0
!nativeeditor_status => inserted
Incorrect field name used: sortorder
data
text => test with branch ordering
start_date => 2013-10-15 01:00:00
duration => 4
progress => 0.25
parent => 89
id => 1382954147351
end_date => 2013-10-19 01:00:00
owner => 0
conge => 0
!nativeeditor_status => inserted
Incorrect field name used: sortorder
data
text => test with branch ordering
start_date => 2013-10-15 01:00:00
duration => 4
progress => 0.25
parent => 89
id => 1382954147351
end_date => 2013-10-19 01:00:00
owner => 0
conge => 0
!nativeeditor_status => inserted
INSERT INTO gantt_tasks(`start_date`,`end_date`,`text`,`duration`,`progress`,`sortorder`,`owner`,`conge`,`parent`) VALUES ('2013-10-15 01:00:00','2013-10-19 01:00:00','test with branch ordering','4','0.25','','0','0','89')
SELECT MAX(sortorder) as maxvalue FROM gantt_tasks
exception 'Exception' with message 'MySQL operation failed
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'maxvalue FROM gantt_tasks' at line 1' in E:\wamp\www\gantt\codebase\connector\db_common.php:1085
Stack trace:
#0 E:\wamp\www\gantt\codebase\connector\db_common.php(747): MySQLDBDataWrapper->query('SELECT MAX(sort...')
#1 E:\wamp\www\gantt\codebase\connector\db_common.php(659): DBDataWrapper->queryOne('SELECT MAX(sort...')
#2 E:\wamp\www\gantt\codebase\connector\dataprocessor.php(170): DBDataWrapper->new_record_order(Object(DataAction), Object(DataRequestConfig))
#3 E:\wamp\www\gantt\codebase\connector\dataprocessor.php(97): DataProcessor->inner_process(Object(DataAction))
#4 E:\wamp\www\gantt\codebase\connector\base_connector.php(491): DataProcessor->process(Object(DataConfig), Object(DataRequestConfig))
#5 E:\wamp\www\gantt\codebase\connector\gantt_connector.php(128): Connector->render()
#6 E:\wamp\www\gantt\codebase\connector\base_connector.php(410): GanttConnector->render()
#7 E:\wamp\www\gantt\samples\common\connector.php(10): Connector->render_table('gantt_tasks', 'id', 'start_date,end_...', '')
#8 {main}
Edit operation finished
0 => action:error; sid:1382954147351; tid:92;
Done in 0.046864032745361s
====================================
Log started, 28/10/2013 09:56:16
====================================
SELECT `id`,`start_date`,`end_date`,`text`,`duration`,`progress`,`sortorder`,`owner`,`conge`,`parent` FROM gantt_tasks ORDER BY sortorder
SELECT `id`,`source`,`target`,`type` FROM gantt_links
Done in 0.015621185302734s