VPN tunneling shutting down

Hi, I have configured a lot of FortiGate VPN tunneling for customers, and today I' m stuck by a VPN tunneling which shutting down 4 or 5 times per day. Everything is good customer can join his second FortiGate by VPN, and sometimes he cant, he call me and I see on the monitor " click to bring up" -_-. I do it, then everything is working, customer can connect again. (first time I see that) Anyone get a solution about this ? PS : Fortigate 50B and I already did : -------------------------- #dia vpn tunnel list If tunnel is not coming up, please connect FGT through any SSH application like Putty and return below commands output when try to bring the tunnel up through the GUI. diag deb dis diag deb reset diag debug enable diag debug console timestamp en diag vpn ike log-filter dst-addr4 <public ip of the vpn peer> diag debug application ike -1 -------------------------- and : #config system global #set phase1-rekey enable -------------------------- Best regards