미국 E2비자에서 I 797B 그런데 왜 797B로 받았는지 모르겠습니다.

I-797B means a consular process that you need to go out of the US, get a Visa stamp, and come back to the US.
It is required usually when a change of status is not allowed in your condition or you have lost non-immigrant visa status.
Ask your corporate law firm for more detail.