NRI cannot buy SBI shares online?

I tried to buy SBI shares online from my NRI account. It gives message that NRI cannot buy SBI shares.

Does anybody know since when this change is made or reason for it. I can buy other PSU banks as well as private banks from same account.

limit is 20 per cent of the paid up capital in the case of public sector banks, including the State Bank of India.

SBI has reached that limit so NRI cannot buy

thanks