Naturally, I attempted to SSH into the VE in question, but was unable to connect. I then SSHed into the physical server and attempted to run the following command to get into the VE:
This popped up the following message:
vzctl enter 236
Oh boy. Now what? A Google search seemed to indicate that the problem was with the udev system inside of the VE. Further research produced a couple of commands that I tried:
enter into CT 236 failed Unable to open pty: No such file or directory
That removed the udev code from the startup scripts so that it would no longer be run. Then I restarted the VE.
vzctl exec 236 update-rc.d -f udev remove
Bingo! Now I was able to enter the VE, and Nagios was able to connect and monitor its status.
vzctl restart 236