Originally Posted by Flying Bosun

142500 miles will just cover your 2 legs in J if they are Q2.
You will need 179000Qmiles if F from CDG is x2 and J from DOH is x1.

When mixing classes and/or Qmiles X1 or 2 then the webpage just cant do the math correct but will show a fault message after next step.
In your case you will have to look for a X1 in J from DOH when you want to fly First at doubble Qmiles out from CDG.

Cheers