THANKS admin for letting me reply to help people.Here is the fix 100% working.
Just install three SimmConnect installers:
Flight Simulator SimConnect Client v10.0.61259.0 Flight Simulator SimConnect Client v10.0.61242.0 Flight Simulator SimConnect Client v10.0.60905.0
These can be found in installation directory of FSX->SDK->->CoreUtilitiesKit->SimmConnectSDK->LegacyInterfaces.
Install all three and REBOOT computer(this is must).
Reason if u install Prepar3d before FSX the prepar3d does not install simmconnect correctly.So install FSX before Prepar3d.Hope it helps
EDIT:
If you have prepar3d installed then installation directory-.>Redist->Interface
(location of three SimmConnect installers)