Reply to help with adding decks to tractor le 2

Hi i am new here

i have recently purchased a ndx900 x decks and a 3 channel mixer

i have also installed traktor le 2 i have read the instructions and came to a dead end that has had me mind boggled for 2 days now...

Its quite simple to explain. simply i am using two decks and i can only add one. the add button for some reason is grayed out.

any help would would be much appreciated

if you need anymore info just ask

thanks