FBInstant.shareAsync is not working from the second html page

Question

actually game starts from first.html ,there is a button in the first.html which redirect to second.html, and there is a share button in the second.html which triggers 'FBInstant.shareAsync()' function.....the problem is that the shareAsync funtion is not working from there. But when I start the game from Second.html directly(not from frist.html) by putting the url of Second.html the ShareAsync function is working fine...I found that FBInstant is not loaded in second.html(showing null in console),plz help me to resolve this problem