Creating a task in Arma 3 with a custom icon.

In description.ext

    class CfgTaskTypes
    {
    class Attack
    {
        icon     = \A3\UI_F_MP_Mark\Data\Tasks\Types\Attack_ca.paa;
        icon3D   = \A3\UI_F_MP_Mark\Data\Tasks\Types3D\Attack_ca.paa;
    };
    class Annex
    {
        icon = a3\ui_f\data\Map\Markers\NATO\o_mech_inf.paa;
        icon3D = a3\ui_f\data\Map\Markers\NATO\o_mech_inf.paa;
    }
    class Warlord
    {
        icon = a3\ui_f\data\Map\VehicleIcons\iconManCommander3_ca.paa;
        icon3d = a3\ui_f\data\Map\VehicleIcons\iconManCommander3_ca.paa;
    }
    class Tower
    {
        icon = a3\ui_f\data\Map\MapControl\transmitter_CA.paa;
        icon3d = a3\ui_f\data\Map\MapControl\transmitter_CA.paa;
    }
    class Defend
    {
        icon     = \A3\UI_F_MP_Mark\Data\Tasks\Types\Defend_ca.paa;
        icon3D   = \A3\UI_F_MP_Mark\Data\Tasks\Types3D\Defend_ca.paa;
    };
    };

In the function that inits the AO.

    [west, ["task3"],["Counter enemy invasion.", "Destroy the enemy.", "Destroy all enemy forces."], [objNull, true], "ASSIGNED", 1, true, "Annex", true] call BIS_fnc_taskCreate;

This is how I got it to work just fine. I am using the task type "Annex".