Can you provide more specific information? It sounds like you're talking about a top coat or coats of bottom paint
applied over existing older bottom paint
, and that the new paint is blistering on top of the old paint, and that the old paint is intact under the blister. Also, what form does the blister take? Is it an actual raised blister, or is the paint simply coming off?
What was the old paint and what is the new paint? How was the surface prepared?
If you know for certain that the old paint and the new paint are compatible (and that does not mean in terms of types of paint but actual manufacturers' stated compatability), sounds like a preparation issue or what Illusion said.