Tunnel not holding connection

Morning everyone 
i have just updated my node to the latest image 
node is a ubnt (bullet-m) the network that we run is based on HSMM 
the server is HSMM tunnel server.
i can see it connect then drop the connection 
her is the log from logread

Sun Apr 25 03:23:16 2021 daemon.info vtund[999]: Connecting to *****.ddns.net
Sun Apr 25 03:23:16 2021 daemon.debug vtund[999]: Remote Server sends <TuL9KE> .
Sun Apr 25 03:23:16 2021 daemon.info vtund[999]: Remote server using older encryption.
Sun Apr 25 03:23:16 2021 daemon.info vtund[999]: Session VK6EEE-172-31-221-52[*****.ddns.net] opened
Sun Apr 25 03:23:16 2021 daemon.notice netifd: Interface 'tun60' is enabled
Sun Apr 25 03:23:16 2021 daemon.notice netifd: Network device 'tun60' link is up
Sun Apr 25 03:23:16 2021 daemon.err vtund[999]: Couldn't fork()
Sun Apr 25 03:23:16 2021 daemon.notice netifd: Interface 'tun60' has link connectivity
Sun Apr 25 03:23:16 2021 daemon.notice netifd: Interface 'tun60' is setting up now
Sun Apr 25 03:23:16 2021 daemon.notice netifd: Interface 'tun60' is now up
Sun Apr 25 03:23:16 2021 daemon.info vtund[999]: Session VK6EEE-172-31-221-52[****.ddns.net] closed
Sun Apr 25 03:23:16 2021 daemon.notice netifd: Interface 'tun60' is now down
Sun Apr 25 03:23:16 2021 daemon.notice netifd: Interface 'tun60' is disabled
Sun Apr 25 03:23:16 2021 daemon.notice netifd: Network device 'tun60' link is down
Sun Apr 25 03:23:16 2021 daemon.notice netifd: Interface 'tun60' has link connectivity loss
Sun Apr 25 03:23:17 2021 daemon.info olsrd_hotplug: [OK] ifup: 'tun60' => 'tun60'
Sun Apr 25 03:23:17 2021 daemon.debug olsrd_hotplug: [OK] interface 'tun60' => 'tun60' not used for olsrd


could anyone help with this or give me some idears to try..

thankyou 
regards Martin 
VK6EEE