Hi, just solved the problem....
Its an incompatibility between lightmix V 1.5 and 1.6. So that means that if you reopen an old scene done with lightmix 1.5 in 1.6, many bugs appear, The solution is to make a brand new max scene, and merge yout old one in, redo lighting or just copy from older and re-render.
For the moment it seems to work and no problems anymore with DR either...
Thanks