Audio from shot gun mic problem?

I have a shotgun mic plugged to a Nikon DSLR d5100. We had a mic test shooting this day. After editing it in sony vegas and uploading the video in facebook.weird thing happened… Upon playing it in the fb player, i noticed the part where i did not use the mic is heard but in the part where i used the shotgun mic.nothing can be heard except the background music

other details:

i can hear the shotgun mic audio in the raw video
i can hear the shotgun mic audio while editing in sony vegas
i can hear the shotgun mic audio after i render it
when i play it in my laptop, the uploaded product can be heard (part of the shotgun mic)

my friends can't hear it too in their laptops

Don't know