At current, B will accept ssh connections, but every 30 seconds, it will go to sleep for 30 seconds, and then back again. D will not accept ssh connections until I restart ssh, and then is good for about two minutes, then it dies. A and C are on the same network, and my ssh connections are all from my desktop. Neither has any issue.
I think that a reinstall is not the solution for that. Please edit the root crontab by running "crontab -e" and comment out the server.sh cronjob by adding a # in front. Then wait a few minutes and check if the ssh problem is solved.
Regarding the update you did, how did you install it? Did you install it on the shell by executing the ispconfig_update.sh script or did you install it trough the ispconfig interface?