From the link provided above, it was not clear to me what exactly "disable DayZ" meant. In case others are unsure here is what I had to do to regain the ability to play single player.
First
Launch arma2oa.exe from the install directory.
(Not sure if this is absolutely necessary but the point is to remove any special run parameters or command line script launchers for troubleshooting purposes)
Second
At the initial menu, select "Expansions"
Uncheck the box next to @dayz
Ok
You will be prompted to restart the program
You should now be able to load your single player saved campaign and/or play single player missions.