S.T.A.K.E.R. SoC problem

i am at yantar i think and i need to talk to the professor there but i cant talk to him it wont let me "press f to talk"
i have OL on stalker SoC cause i beat the game and it looked like a good mod and is
i have slightly modded the game (weight what traders sell how much the buy things for)
i have not saved the scientist (the one near the crashed helicopter)
also the guy that takes the rad readings or whatever will talk to me but says he is busy