When there is a loop in your ductwork, Design Master HVAC cannot calculate the CFM. If you cannot locate the loop based upon the information provided by the error, use the “Coordinate” command on the drawing. It is possible that a duct in the database but not currently on the drawings is causing the problem.
If you have ductwork that actually have a loop in it, you need to model it in DM HVAC so that it does not have a loop. You need to choose a middle point in the loop, and draw the ductwork from two sides toward that point. Have the end points of the two ducts meet at this location. Use the “DM HVAC->Fittings->No Fitting” command and select the end of the two ducts that meet. This will remove the end cap fitting from each of the ducts and they will appear to be a continuous section.