what does I797b mean after getting a 221g

[magizh]

Hi
In my case I was in US got my H1b after being on F1. I travelled to India for my visa stamping with a I797a. I got a 221g on Nov 12th and it is still under administrative processing. Meanwhile my employer got a I797b approved on Dec 10th . Till date I don't see the status change for my 221g. What should I do now. What does receiving a I 797b when I have I 797a mean ?

Thanks for any help!
Magizh