You have layers of urethane under it so use lacquer thinner,put it in a spray bottle and mist it on,let it soak for 3-5 minutes,it will tack up very quickly,once it does,keep spraying it,the white will begin to run off,once its gone,immediately neutralize it with denatured alcohol and you'll be fine! I see it from time to time at work and that's how I get rid of it. The white usually comes from moisture in the wood or the previous coat wasn't dry yet,it will work trust me! if you've no alcohol water will suffice. Ron