ok my bad i was trying to engineer a guardian power plant and distributor that is why it did not let me i did not know that they are not engineered ,thanks for the time,my bad
I see the PD is not available on the Dweller's 'able to engineer' module list. This could be a bug in the PD module; I would store it and then install the module. I suggest this because it could be related to the hardpoint bug that causes your fire groups to not work; and uninstalling and installing corrects that bug/error.