I am stuck on this mission. I am unable to go anywhere with this thing because there is no option to talk to Hildren about it because I unknowingly completed "There Stands a Tall Grass." Does anyone know a work around to get Hildren to talk? Without completing this mission, I can't recruit Cass.

I am sorry to tell ya.......
but if you have completed "There Stands the Grass" quest, Doctor Hildern might glitch and not accept your parcel.
There is no known way to correct the lack of an option to give Dr Hildern the invoice at the moment...
:vaultboy:

Everything I have read about that glitch says the same thing but I was hoping there was something to be done. I guess I should count my self lucky to have this be my only big issue with the game thus far and I am pretty far in the game. It is one thing when a glitch makes you die unnecessarily or you have to reload a save but when it causes you to not be able to advance in a storyline I think that is pretty crappy.