Can't unlock M249

I cannot unlock the M249, no matter what I do. Cannot unlock the assignment either. I know there are a lot of posts with similar problems, but there is no solution to it yet. So, maybe, if more people will write about it, this f..ckn DICE will fix this. I mean, small bugs or glitches are ok, as the game itself is very good, I think. But making it impossible to unlock a weapon is kind of unfair. So, please, if you have the same or similar problem, do make a note in the comments, or create your own thread on this.