I thought I did everything right. I wanted to repaint some 50 year old dark wood paneling in my den. I cleaned the paneling with TSP. I spackled to fill in all the grooves. I used an electric sander to rough up everything and smooth out all of the spackle. I then painted with primer. The primer is dry but there are spots where I can scrape it off with my thumb nail. I thought I did everything right. What is wrong and how do I fix it?