about stock options.

I have worked for my current employer for more than 4 years. On the first day of my employment, I signed a stock options contract (Nonstatutory Stock Option Agreement) with my employer. Now four years have passed and all shares have been vested.

My company is still a private company that I do not expect it go public for a very long time. However, recognizing the potential of the company I want to exercise my options. My employer told me that I can not do so because I am neither a citizen nor a permenent resident. Here are my questions:

1. Is it true that people like I (H1Ber) can not exercise stock optioins of private companies ?
2. If yes, since I have four years to exercise stock options from now on, can I exercise stock options after I obtained my green card ?

Thanks