*Tunnelblick: OS X 10.13.0; Tunnelblick 3.7.1a (build 4812)
2017-06-20 12:48:26 *Tunnelblick: Attempting connection with us-08.protonvpn.com.udp1194; Set nameserver = 769; monitoring connection
2017-06-20 12:48:26 *Tunnelblick: openvpnstart start us-08.protonvpn.com.udp1194.tblk 1337 769 0 3 0 1065264 -ptADGNWradsgnw 2.4.2-libressl-2.5.0
2017-06-20 12:48:27 *Tunnelblick:

Could not start OpenVPN (openvpnstart returned with status #251)

Contents of the openvpnstart log:
*Tunnelblick: openvpnstart log:
OpenVPN returned with status 1, errno = 0:
Undefined error: 0

Command used to start OpenVPN (one argument per displayed line):

/Applications/Tunnelblick.app/Contents/Resources/openvpn/openvpn-2.4.2-libressl-2.5.0/openvpn
–daemon
–log
/Library/Application Support/Tunnelblick/Logs/-SLibrary-SApplication Support-STunnelblick-SShared-Sus–08.protonvpn.com.udp1194.tblk-SContents-SResources-Sconfig.ovpn.769_0_3_0_1065264.1337.openvpn.log
–cd
/Library/Application Support/Tunnelblick/Shared/us-08.protonvpn.com.udp1194.tblk/Contents/Resources
–verb
3
–config
/Library/Application Support/Tunnelblick/Shared/us-08.protonvpn.com.udp1194.tblk/Contents/Resources/config.ovpn
–verb
3
–cd
/Library/Application Support/Tunnelblick/Shared/us-08.protonvpn.com.udp1194.tblk/Contents/Resources
–management
127.0.0.1
1337
–management-query-passwords
–management-hold
–script-security
2
–up
/Applications/Tunnelblick.app/Contents/Resources/client.up.tunnelblick.sh -9 -d -f -m -w -ptADGNWradsgnw
–down
/Applications/Tunnelblick.app/Contents/Resources/client.down.tunnelblick.sh -9 -d -f -m -w -ptADGNWradsgnw

Contents of the OpenVPN log:

Options error: Temporary directory (–tmp-dir) fails with ‘/var/folders/jd/mpgwyrw138d5y_cqz0bzhz7m0000gn/T/’: Operation not permitted
Options error: Please correct these errors.
Use –help for more information.

More details may be in the Console Log’s “All Messages”