paint problems  

Anyone here that knows about paint? I tried to paint a chassis having a unknown paint. Mostly one coat that has peeled away from the metal. I'm using some oil based universal tractor paint. The oil based would not bond, it turned to a gel like rubbery grease. 2 days later and it is still spongy and soft. All that damn sanding and elbo grease down the tubes. Any clues as to what happened?  I sure don't want to go through this again.   Thanks...