<key>StandardOutPath</key>
<string>/var/log/WebObjects/webobjects.log</string>
<key>StandardErrorPath</key>
<string>/var/log/WebObjects/webobjects.log</string>
Because /var/log isn't writable by appserver, the user under which wotaskd and JavaMonitor run, /var/log/webobjects.log can't be created by wotaskd or JavaMonitor. I suppose that you could
sudo touch /var/log/webobjects.log
sudo chown appserver:appserverusr /var/log/webobjects.log
but for me, it was safer to
sudo mkdir /var/log/WebObjects
sudo chown appserver:appserverusr /var/log/WebObjects
which will then allow wotaskd and JavaMonitor to create and write /var/log/WebObjects/webobjects.log whenever necessary without manual intervention.