Hi

Yesterday it happened to me too and no matter what i did, i still couldn't collect it even if i started i new campaign.
So, i removed all the saved games, and every data saved by my profile.
I must admit that i didn't get to kill any alien already to see if it works because i started a new campaign.
Possible fixes.
1. Remove everything that's in this folder C:\Users\YourUserName\Saved Games\Crysis2
Or
2.Make a new Profile in the game.

Good luck

Bump, so the people can see it and try it.