Hey!
I compiled TUN 1.1 driver on my Solaris 10 64bit, and everything was working fine, all the commands for installation were successfull (add_drv, devfsadm -i tun ... etc.)
and the driver was working fine as I got OpenVPN server up and running with successful clients attached. My only problem is that when I reboot the system now it will crash and instantly reboot again... and again in the neveredning loop until I boot failsafe, mount the root file system and remove this tun driver from /usr/kernel/drv/amd64/
Then the system boots fine and I can install again the driver and use it. Until next reboot of course 
Any hints for me what could have I missed ?
What's the error message in /var/adm/messages?
it worked fine (the reboot) after I at first had stopped the openvpn manually before I issued 'init 6'