Posting not possible and DB error

[Ordovicium]

I am facing the issue, that no one can post anymore. Getting following error by mail:

Database error in vBulletin 5.2.3:

                        Invalid SQL:
INSERT  INTO closure (`parent`,`child`,`depth`,`publishdate`)
                        VALUES(1361570,1361570,0,1474486866)
/**closure**/;

                        MySQL Error   : Duplicate entry '1361570-1361570' for key 'closure_uniq'
                        Error Number  : 1062
                        Request Date  : Wednesday, September 21st 2016 @ 09:41:06 PM
                        Error Date    : Wednesday, September 21st 2016 @ 09:41:07 PM
                        Script        : http:///create-content/text/
                        Referrer      :
                        IP Address    :
                        Username      : Briefkasten
                        Classname     : vB_Database_MySQLi
                        MySQL Version :

[Ordovicium]

Forget about this issue. I switched back to vB4, because I am facing so many issues with vb5. Hopefully a later version will bring more stability.