Painted latex over veneer particle board... disaster

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Hey everone
I am kind of in a mess here , I sanded, primed and painted three bookshelves for my sons firestation theme room with latex paint , now when I am done assembling the third and the last one I saw a spot and sanded to apply primer and paint , it started peeling off like plastic , I have been doing this for three days , I am exhausted, worn out and sad... Please , please please, tell me any way I could secure this paint... something in the world needed...

Other info. The furniture , I bought from target , is veneer covered on particle board... the paint did not stick on it so I used primer , the krylon spray one, and used behr , primer/paint in one paint...
Can anybody help