This has been discussed several times before as well. Just create a dummy operating unit and assign it to the Site level and to your GL responsibility using the profile option MO: Operating Unit.
Recurring journal and mass allocation feature expects that you have assigned an operating unit to the GL. If you are not planning to use subledger then simply create a dummy OU and assign it. You can view first few AP videos to find out how to create OU.
http://handsonerp.com/forum.html?func=view&id=2230&catid=2#2230