Thanks a bunch MrCoolz for your comments. I went to murthy.com and found 2-3 postings regarding job change in their archive. Her ansers were different for same questions. See the following post.
Question : Can one change multiple jobs using AC21 after having completed 6 months into the I-485 with one"s sponsoring employer ?
Answer : Without any AC21 regulations, one is not clear when the BCIS will actually approve the I-485 even with only one change in employers. With each additional change in employers there is an added risk of a potential problem or RFE by the BCIS. Of course, all of the jobs must be considered the "same or similar" to be eligible for porting under AC21 since, if the BCIS issues an RFE, one should be able to demonstrate eligibility under the law.
Please let me know if you are confortable with my question....
Did you change your employer 2 times using AC21? If yes what are the steps or documents did you use to notify BCIS?