Paint incompatibility can cause loss of adhesion where many old coats of alkyd or oil-based paint receive a latex topcoat. 
What Causes It?When water-based latex is painted over more than three or four coats of old alkyd or oil-based paint, the old paint may “lift off” the substrate.
How to Solve ItRepaint the surface using another coat of alkyd or oil-based paint. Alternatively, you can completely remove the existing paint and prepare the surface—cleaning, sanding, and spot-priming where necessary—before repainting with a top-quality latex exterior paint.

Note: Images provided by The Rohm & Hass Paint Quality Institute.