I know this question has been asked a lot of times. I read a lot of the other threads too.
My case is that I was on OPT from Aug 06 to Oct06. Then H-1B. My employer deducted SSN and medicare for the time I was on OPT as well.
The employer claims that they could have refunded me last year but now its too late and I need to get the refund from IRS.

So. I have to file i843. My questions are -

1.Since, I was on OPT for about 5 weeks - 2.5 paychecks, how do I calculate the SSN and MEdicare tax? What proof do I give IRS? Should I send a copy of my paystubs?

2. For the explanation of the reason, do I have to cite any articles etc? If yes, which ones? My country doesn't have a totalization treaty (which I am assuming is valid on H-1B only).

I really appreciate your help.

Thanks!!

1) Determine what your daily wage is by dividing your annual income by the total number of days worked. Multiply the daily wage by 6.2% for Social Security and 1.45% for Medicare, then multiply the result by the five weeks in OPT.

All of the required documents is listed on page 48 of IRS Pub 519.

2) No need to cite a treaty article. Cite IRS Pub 519.

Thank you Atlanta tax expert! That was of great help!
One more quick question - Pub 519 says that I need to send a copy of the visa - I am guessing its my F-1 visa with the I-20. Do I need to send a copy of my H-1B as well (which is obviously more recent)?

Send them BOTH (F-1 and H-1B). You send the F-1 to prove you are entitled to the refund, and the H-1B to substantiate your calculations.