This article explains what to do when you turn on auto update and you have a booking with no available rooms. Doing this will allow you to run auto update without further errors. You will still need to contact the guest after the reservation has been cancelled.
1. Turn off Auto-Update.
2. Go to Tools> Unit and Rate Setup> Individual Units
3. Change the number of active units in the top to one more unit than you actually have.
4. Turn auto update back on by clicking the "X" in the lower right hand cover of the Reserve by Day screen. The new reservation will go into the new available room.
5. Now you can delete the reservation. After deletion you will need to go back to Tools>Unit and Rate Setup> Individual Units and put the number of active units back to the correct number.