Atomizers need an initial guess of downstream pressure/density. For that Fluent calculates the virtual origin based on Position (x,y,z), Injector Inner Diameter and Spray Half Angle. This point is used for evaluating an initial guess of downstream pressure/density. If this virtual origin is found outside of the domain you will get the warning message reported. If you move the center point of your atomizer (X,Y,Z-Position) slightly into your domain, the warning disappears and the particles are injected as intended.