Quick search came up with this:
Woods like cocobolo have a certain amount of natural-occurring oil in them. When you coat them with an oil-based finish, the oil in the wood itself prevents the finish from oxidizing and curing properly. So you have a few options. You can either use something like shellac or lacquer instead of an oil-based finish. Or, we can seal the wood first, preventing the oil from contacting the oil based finish. Shellac is a great sealer for this purpose. A good coat of a 2lb cut (I use Bullseye Sealcoat) dewaxed shellac should do the trick. Sand lightly with 320 after the shellac and proceed with your oil-based finish. Now keep in mind you want a straight varnish at this point (not an oil/varnish blend). But you should have no adhesion issues with the varnish at that point.
