I was employed on student visa in Sep 2007 (exempt from Social Security tax) and in Oct 2007 I started my H1-B visa, but my Sep 2007 salary was paid in Oct, does it mean that I have to pay social security tax on my september salary (just because it was paid in Oct.)

I am just curious "Doctrine of Constructive Receipt" should not be applicable here, since it is a matter of taxability of wages?

" I was employed on student visa in Sep 2007 (exempt from Social Security tax) and in Oct 2007 I started my H1-B visa, but my Sep 2007 salary was paid in Oct, does it mean that I have to pay social security tax on my september salary (just because it was paid in Oct.)"---->No; you, as a F1 visa holder, were exempt from your FICA Taxes up to Oct 2007, when you became a H1B visa holder, and you became liable for FICA (Social Security and Medicare) taxes the day your H-1B visa became effective.I this case, Oct. 2007. So you should pay your FICA Taxes on your Oct. paycheck that you received as a H1B visa holder.The exemption from paying your FICA Taxes should have ended when you converted to the H-1B visa, Oct. 2007.