I will be tiling my kitchen floor and will be putting down 1/4" backerboard over 3/4 plywood sub floor part of the floor has black cut back adhesive I was told by a professional tiler that I should use a ready to use mastic adhesive under the backerboard instead of versabond. Then use versabond for tile application. Is this an OK application?

A professional told you that? Why on earth? Use thin set like Versabond to install the CBU, then Versabond again, or a better mortar for the tiles. BTW, are you sure the cutback is on "the" subfloor and not a 1/4" underlayment? VCT or VAT tiles should have not been installed over the subfloor, should be a second sheet of ply. Did you check it out?

Jaz

Yes, The vinyl tiles were put directly over the subfloor. As far as using a mastic it really didn't make much sense so I thought I would ask another professional. The professional who gave me the information has been in the business for 20 years.
Thanks for the information and will follow your advise.