Administration - Installation - Core: Installaton issus with oracle db

When I install ilias with oracle  database, I got an issue as such error message:

ilDB Error: addUniqueConstraint(dav_lock)

MDB2 Error: unknown error
_doQuery: [Error message: Could not execute statement] [Last executed query: ALTER TABLE dav_lock ADD CONSTRAINT dav_lock_c1_idx UNIQUE (token)] [Native code: 2261] [Native message: ORA-02261: such unique or primary key already exists in the table]
#0 /var/www/html/Services/Database/classes/class.ilDB.php(1103): ilDB->handleError(Object(MDB2_Error), 'addUniqueConstr...')
#1 /var/www/html/setup/sql/ilDBTemplate.php(15599): ilDB->addUniqueConstraint('dav_lock', Array, 'c1')
#2 /var/www/html/setup/classes/class.ilSetup.php(377): setupILIASDatabase()
#3 /var/www/html/setup/classes/class.ilSetup.php(278): ilSetup->readDump(Object(ilDBOracle), './setup/sql/ili...')
#4 /var/www/html/setup/classes/class.ilSetupGUI.php(2764): ilSetup->installDatabase()
#5 /var/www/html/setup/classes/class.ilSetupGUI.php(466): ilSetupGUI->installDatabase()
#6 /var/www/html/setup/classes/class.ilSetupGUI.php(283): ilSetupGUI->cmdClient()
#7 /var/www/html/setup/classes/class.ilSetupGUI.php(144): ilSetupGUI->cmdAdmin()
#8 /var/www/html/setup/setup.php(52): ilSetupGUI->ilSetupGUI()
#9

Can anyone tell me how to solve this? Thanks...

My env as such:

1. ilias 5.1.13;


2. oracle 12c;


3. centos7;


4. apache 2.4.6;


5. php 5.6.29;