Queen v Norton 2006

Dear SirsRe 747 and Norton 2006After installing Norton I have found out to my dismay this as affected 747, on the climb out I have a problem with aircraft holding the climb rate.Even if I reach the pre determined height, I still have the problem of holding that height.Prior to starting flight sim I disarm Norton and its FirewallI have pre-set the trim in the FMC Gear and Flaps Up15% Climb Rate set before selecting VNavClimb rate also affects FLCHStarting no problemTaxing no problemTake-off no problemLanding no problem I have also deleted all the saved flights, and started a fresh.Any advice will be welcome.Duncan