I’ve found that waking my mac from suspend in a different network than it went to sleep in can crash tunnelblick, or cause tunnelblick to try to spin up another openvpn instance, leaving the network wedged. The workaround is to invoke this in a terminal:

sudo killall -v openvpn

then relaunch tunnelblick.

If that doesn’t work, force-unloading the kernel extension does the trick:

sudo killall -v openvpn
sudo killall -v Tunnelblick
sudo kextunload -b foo.tun

then relaunch tunnelblick.