How to generate primitive colissions for GTA V using Collider Tools [GTA V MLO Tutorial] 

you have to creat them first on any prop, so that you can select them in collider tools afterwards

I never had that error myself. Maybe you can try to contact the creator and ask him for advice.

​@@maxjohanni i did, waiting for the answer. if it wouldnt be hard for you, could u tell what is your hardware? i was searching for the solution on VHACD github page and, well, didnt understand a single word there but it seems to me that this error might be hardware-related