Honestly, you didn't need to do all of that.
%error = forceRequiredAddOn("Vehicle_Jeep");
if(%error == $Error::AddOn_Disabled)
{
JeepVehicle.uiName = "";
}
if(%error == $Error::AddOn_NotFound)
{
error("ERROR: Vehicle_SlowJeep - required add-on Vehicle_Jeep not found");
return;
}
datablock WheeledVehicleData(SlowJeepVehicle:JeepVehicle)
{
uiName = "Slow Jeep ";
maxWheelSpeed = 10;
};
would suffice.
Anyway, aside from that your file is a RAR file. It needs to be a ZIP file.
EDIT: added forceRequiredAddOn