QTR-Quadtone RIP

I am trying to linearize my UT7 curve and getting "Not constantly 
increasing" error after I entered my linearization data. What does it 
mean? My densities are increasing, sure not constantly, I mean not 
linear, but it is not what is expected here, right? I did linearized 
some data for the other printer, it is not quite clear what is 
expected in this module. How much linearization is supposed to be done 
manually before this step?

Thanks,
Sergei