Crono, vbe3 is not good to use as it still is almost unsupported on many newer cards even of the new generations.

Are you sure you know what you are doing. According to Ralf Brown's interrupt list, function 4f06 is get/set logical scanline length and 4f07 is also something with scanlines. Sounds rather funky to me. Are you sure this is what you want. Those commands should be well supported either way as they are part of the VBE 1.1 specification.

Try to show us some code