Dismount the window screen to make it easier to manage during the removal process. Lay it down on a flat surface in an open area.
Attempt to scrub the affected area with water and a cleaning brush before applying a stronger solvent. Fresh latex can take weeks to develop full adhesion and often comes loose with some water.
Wet the latex paint and apply isopropyl alcohol to the area with a dry rag. Cover the surface with any sheet of plastic to prevent evaporation.
Rinse the area with water after a short period of time and the latex paint will wash off.