Did you paint the zinc chromate on? If this is an older airplane, VeriPrime was a DuPont product that was a two-part epoxy and will STICK. My airplane was pained with VeriPrime in anticipation of me painting it someday. That was in 1997. She has flown since then, including sitting in the Sun for events like, say, OSH, and has shown no signs of the primer parting company with the airplane. If it is a two part, you might just need surface prep as above. Otherwise you might need to....erk....erk......erk......remove it.....IMHO...Try wiping the zinc chromate with a solvent such as MEK or acetone. If it immediately attacks and softens you most likely will have compatibility issues with urethane topcoats and even epoxy primers, best to just completely remove and start over. If it passes the solvent test and appears to be a sound coating you could thoroughly clean, scuff, epoxy prime and top coat.