Dears, first of allo sory for my non perfect english.
I have a problem.
In the mission "I'll know when it will happen" and exactly when I go talk to the mercenary Grant, once an open dialogue with him, nothing happens, and I find myself not knowing what to do. Can you help please? Thanks

maybe isa bug?? when u play fot the NRC and do to talk with mercenary Grant, wich are their answers??

First don't worry about your english.
http://fallout.wikia.com/wiki/You%27ll_Know_It_When_It_Happens will help you.